Showing papers on "Gallium nitride published in 2006"
TL;DR: Repeated application of an additive, transfer printing process that uses soft stamps with these substrates as donors, followed by device and interconnect formation, yields high-performance heterogeneously integrated electronics that incorporate any combination of semiconductor nanomaterials on rigid or flexible device substrates.
Abstract: We developed a simple approach to combine broad classes of dissimilar materials into heterogeneously integrated electronic systems with two- or three-dimensional layouts. The process begins with the synthesis of different semiconductor nanomaterials, such as single-walled carbon nanotubes and single-crystal micro- and nanoscale wires and ribbons of gallium nitride, silicon, and gallium arsenide on separate substrates. Repeated application of an additive, transfer printing process that uses soft stamps with these substrates as donors, followed by device and interconnect formation, yields high-performance heterogeneously integrated electronics that incorporate any combination of semiconductor nanomaterials on rigid or flexible device substrates. This versatile methodology can produce a wide range of unusual electronic systems that would be impossible to achieve with other techniques.
715 citations
Journal Article•
TL;DR: In this paper, a new and general strategy for efficient injection of carriers in active nanophotonic devices involving the synthesis of well-defined doped core/shell/shell (CSS) nanowire heterostructures was reported.
Abstract: We report a new and general strategy for efficient injection of carriers in active nanophotonic devices involving the synthesis of well-defined doped core/shell/shell (CSS) nanowire heterostructures. n-GaN/InGaN/p-GaN CSS nanowire structures were grown by metal-organic chemical vapor deposition. Electron microscopy images reveal that the CSS nanowires are defect-free single crystalline structures, while energy-dispersive X-ray linescan profile studies confirm that shell thickness and composition can be well controlled during synthesis. Photoluminescence data further show that the optical properties are controlled by the CSS structure with strong emission from the InGaN shell centered at 448 nm. Importantly, electrical devices made by simultaneously contacting the n-type core and outer p-type shell of the CSS nanowires demonstrate that in forward bias these individual nanowires behave as light-emitting diodes (LEDs) with bright blue emission from the InGaN shell. The ability to rationally synthesize galliu...
545 citations
TL;DR: In this article, the authors reported triggered single-photon emission from gallium nitride quantum dots at temperatures up to 200 K, a temperature easily reachable with thermo-electric cooling.
Abstract: Fundamentally secure quantum cryptography has still not seen widespread application owing to the difficulty of generating single photons on demand. Semiconductor quantum-dot structures have recently shown great promise as practical single-photon sources, and devices with integrated optical cavities and electrical-carrier injection have already been demonstrated. However, a significant obstacle for the application of commonly used III–V quantum dots to quantum-information-processing schemes is the requirement of liquid-helium cryogenic temperatures. Epitaxially grown gallium nitride quantum dots embedded in aluminium nitride have the potential for operation at much higher temperatures. Here, we report triggered single-photon emission from gallium nitride quantum dots at temperatures up to 200 K, a temperature easily reachable with thermo-electric cooling. Gallium nitride quantum dots also open a new wavelength region in the blue and near-ultraviolet portions of the spectrum for single-photon sources.
417 citations
TL;DR: In this paper, a GaN/ultrathin InGaN/GaN heterojunction was used to provide a backbarrier to the electrons in an AlGaN and GaN high-electron mobility transistor (HEMT).
Abstract: A GaN/ultrathin InGaN/GaN heterojunction has been used to provide a back-barrier to the electrons in an AlGaN/GaN high-electron mobility transistor (HEMT). The polarization-induced electric fields in the InGaN layer raise the conduction band in the GaN buffer with respect to the GaN channel, increasing the confinement of the two-dimensional electron gas under high electric field conditions. The enhanced confinement is especially useful in deep-submicrometer devices where an important improvement in the pinchoff and 50% increase in the output resistance have been observed. These devices also showed excellent high-frequency performance, with a current gain cut-off frequency (f/sub T/) of 153 GHz and power gain cut-off frequency (f/sub max/) of 198 GHz for a gate length of 100 nm. At a different bias, a record f/sub max/ of 230 GHz was obtained.
384 citations
TL;DR: In this article, epitaxial structures which modify the distribution of guided modes were introduced to enhance the potential for efficient light extraction by photonic crystal assisted gallium nitride light-emitting diodes.
Abstract: We relate the currently limited efficiency of photonic crystal (PhC)-assisted gallium nitride light-emitting diodes (LEDs) to the existence of unextracted guided modes. To remedy this, we introduce epitaxial structures which modify the distribution of guided modes. LEDs are fabricated according to this concept, and the tailored band structure is determined experimentally. We investigate theoretically the consequences of this improvement, which significantly enhances the potential for efficient light extraction by PhCs.
203 citations
TL;DR: Nanowires of the wide band-gap semiconductor gallium nitride (GaN) have been shown to act as room-temperature uv lasers and significant shifts are observed during optical pumping of a ring resonator nanolaser compared to its linear counterpart.
Abstract: Nanowires of the wide band-gap semiconductor gallium nitride (GaN) have been shown to act as room-temperature uv lasers Recent advances in nanomanipulation have made it possible to modify the shape of these structures from a linear to a pseudoring conformation Changes to the optical boundary conditions of the lasing cavity affect the structure's photoluminescence, photon confinement, and lasing as a function of ring diameter For a given cavity, ring-mode redshifting is observed to increase with decreasing ring diameter Significant shifts, up to 10 nm for peak emission values, are observed during optical pumping of a ring resonator nanolaser compared to its linear counterpart The shifting appears to result from conformational changes of the cavity rather than effects such as band-gap renormalization, allowing the mode spacing and position to be tuned with the same nanowire gain medium
191 citations
Patent•
28 Dec 2006
TL;DR: In this paper, the authors proposed a field effect transistor having a structure capable of utilizing a field plate effect (FPE) using a conductive gallium nitride substrate, which comprises a first region 13c having first dislocation density, and a second region 13d having second dislocation densities smaller than the first dislocations density.
Abstract: PROBLEM TO BE SOLVED: To provide a field effect transistor having a structure capable of utilizing a field plate effect SOLUTION: A conductive gallium nitride substrate 13 comprises a first region 13c having first dislocation density, and a second region 13d having second dislocation density smaller than the first dislocation density A gate electrode 17 is provided on a second part 15d of a gallium nitride base semiconductor region 15 A drain electrode 19 is provided on the second part 15d of the semiconductor region 15 A source electrode 21 is provided on the semiconductor region 15, and connected to the second part 15d of the semiconductor region 15 The dislocation density of the first part 15c of the semiconductor region 15 is larger than that of the second part 15d of the gallium nitride base semiconductor region 15 The conductivity of the first part 15c of the semiconductor region 15 is larger than that of the second part 15d of the semiconductor region 15 The source electrode 21 is connected to the first part 15c of the semiconductor region 15 COPYRIGHT: (C)2007,JPO&INPIT
179 citations
TL;DR: In this article, the authors experimentally find that the thermal conductivity of gallium nitride depends critically on dislocation density using the 3-omega technique, and they indicate that the hydride vapor phase epitaxy method offers an attractive route for the formation of semi-insulating gallium Nitride with very low dislocation densities near 5×104cm−2.
Abstract: The authors experimentally find that the thermal conductivity of gallium nitride depends critically on dislocation density using the 3-omega technique. For GaN with dislocation densities lower than 106cm−2, the thermal conductivity is independent with dislocation density. The thermal conductivity decreases with a logarithmic dependence for material with dislocation densities in the range of 107–1010cm−2. These results are in agreement with theoretical predictions. This study indicates that the hydride vapor phase epitaxy method offers an attractive route for the formation of semi-insulating gallium nitride with optimal thermal conductivity values around 230W∕mK and very low dislocation density near 5×104cm−2.
178 citations
Patent•
13 Nov 2006TL;DR: A GaN crystal having up to about 5 mole percent of at least one of aluminum, indium, and combinations thereof is described in this paper, where one grain has a diameter greater than 2 mm and a dislocation density less than about 104 cm−2.
Abstract: A GaN crystal having up to about 5 mole percent of at least one of aluminum, indium, and combinations thereof. The GaN crystal has at least one grain having a diameter greater than 2 mm, a dislocation density less than about 104 cm−2, and is substantially free of tilt boundaries.
165 citations
TL;DR: In this paper, the use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2 A/mm.
Abstract: Enhancement-mode AlGaN/GaN high electron-mobility transistors have been fabricated with a gate length of 160 nm. The use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2 A/mm. The small signal performance of these enhancement-mode devices shows a record current cutoff frequency (f/sub T/) of 85 GHz and a power gain cutoff frequency (f/sub max/) of 150 GHz.
165 citations
Patent•
10 Mar 2006TL;DR: In this paper, a planar, semi-polar nitride film was grown on a miscut spinel substrate, in which a large area of the planar and semi polar nitride was parallel to the substrate's surface.
Abstract: A method for growing planar, semi-polar nitride film on a miscut spinel substrate, in which a large area of the planar, semi-polar nitride film is parallel to the substrate's surface. The planar films and substrates are: (1) {101 1 } gallium nitride (GaN) grown on a {100} spinel substrate miscut in specific directions, (2) { 1013 } gallium nitride (GaN) grown on a {110} spinel substrate, (3) { 1122 } gallium nitride (GaN) grown on a { 1 100 } sapphire substrate, and (4) { 1013 } gallium nitride (GaN) grown on a { 1 1 00 } sapphire substrate.
TL;DR: In this paper, an analysis of ON-state and OFF-state high-electric-field stress results for unpassivated GaN/AlGaN/GaN high-electron-mobility transistors on SiC substrates is presented.
Abstract: Long-term ON-state and OFF-state high-electric-field stress results are presented for unpassivated GaN/AlGaN/GaN high-electron-mobility transistors on SiC substrates. Because of the thin GaN cap layer, devices show minimal current-collapse effects prior to high-electric-field stress, despite the fact that they are not passivated. This comes at the price of a relatively high gate-leakage current. Under the assumption that donor-like electron traps are present within the GaN cap, two-dimensional numerical device simulations provide an explanation for the influence of the GaN cap layer on current collapse and for the correlation between the latter and the gate-leakage current. Both ON-state and OFF-state stresses produce simultaneous current-collapse increase and gate-leakage-current decrease, which can be interpreted to be the result of gate-drain surface degradation and reduced gate electron injection. This study shows that although the thin GaN cap layer is effective in suppressing surface-related dispersion effects in virgin devices, it does not, per se, protect the device from high-electric-field degradation, and it should, to this aim, be adopted in conjunction with other technological solutions like surface passivation, prepassivation surface treatments, and/or field-plate gate
Patent•
31 May 2006TL;DR: In this paper, a planar non-polar m-plane GaN epitaxial layer was grown on a suitable substrate, such as an mplane silicon carbide (m-SiC) substrate, using metalorganic chemical vapor deposition (MOCVD).
Abstract: A method of growing planar non-polar m-plane Ill-Nitride material, such as an m-plane gallium nitride (GaN) epitaxial layer, wherein the Ill-Nitride material is grown on a suitable substrate, such as an m-plane silicon carbide (m-SiC) substrate, using metalorganic chemical vapor deposition (MOCVD). The method includes performing a solvent clean and acid dip of the substrate to remove oxide from the surface, annealing the substrate, growing a nucleation layer such as an aluminum nitride (AlN) on the annealed substrate, and growing the non-polar m-plane Ill-Nitride epitaxial layer on the nucleation layer using MOCVD.
TL;DR: In this article, the electron transport of III-V nitride semiconductors, including gallium nitride, aluminum nitride and indium oxide, has been extensively studied.
Abstract: The III–V nitride semiconductors, gallium nitride, aluminum nitride, and indium nitride, have, for some time now, been recognized as promising materials for novel electronic and optoelectronic device applications. As informed device design requires a firm grasp of the material properties of the underlying electronic materials, the electron transport that occurs within these III–V nitride semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving field, in this paper we review analyses of the electron transport within the III–V nitride semiconductors, gallium nitride, aluminum nitride, and indium nitride. In particular, we discuss the evolution of the field, compare and contrast results determined by different researchers, and survey the current literature. In order to narrow the scope of this review, we will primarily focus on the electron transport within bulk wurtzite gallium nitride, aluminum nitride, and indium nitride, for this analysis. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art III–V nitride semiconductor orthodoxy. A brief tutorial on the Monte Carlo approach will also be featured. Steady-state and transient electron transport results are presented. We conclude our discussion by presenting some recent developments on the electron transport within these materials.
TL;DR: In this paper, an enhancement-mode n-channel GaN high-voltage MOSFET realized on both p and n-GaN epilayer on sapphire substrates is presented.
Abstract: We report on the demonstration of enhancement-mode n-channel GaN high-voltage MOSFET realized on both p and n-GaN epilayer on sapphire substrates. These MOSFETs, with linear and circular gate geometries, show good dc characteristics with maximum field-effect mobility of 167 cm2/Vmiddots, best reported to date
Patent•
05 Sep 2006TL;DR: In this paper, a gallium nitride-based compound semiconductor light-emitting device was presented. But the device required only a low driving voltage (Vf) and was not suitable for light output efficiency.
Abstract: It is an object of the present invention to provide a gallium nitride-based compound semiconductor light-emitting device that is excellent in light output efficiency and needs only a low driving voltage (Vf). The inventive gallium nitride-based compound semiconductor light-emitting device includes an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer formed of a gallium nitride-based compound semiconductor and stacked in this order on a substrate, and positive and negative electrodes so arranged as to be in contact with the p-type semiconductor layer and the n-type semiconductor layer, respectively, wherein a region in which a p-type impurity and hydrogen atoms are co-present exists in the p-type semiconductor layer in contact with the positive electrode, and at least a portion, which is in contact with the p-type semiconductor layer, of the positive electrode, is formed of an n-type electro-conductive light transmitting material.
TL;DR: In this paper, the development of AlGaN-based deep UV light emitting diodes (LEDs) with emission wavelengths from 254 to 340 nm, focusing on the improvement of 280 nm LEDs efficiency was reported.
Abstract: We report on the development of AlGaN-based deep UV light emitting diodes (LEDs) with emission wavelengths from 254 to 340 nm, focusing on the improvement of 280 nm LEDs efficiency. Under optimal device structure the UV LEDs efficiency was found to strongly depend on the AlGaN material quality. Milliwatt-power level LEDs were demonstrated for the 254-340 nm spectral range, and for 280 nm LEDs powers reaching 2.5 mW was achieved at 20 mA DC.
TL;DR: In this paper, the authors have grown GaN and AlGaN nanowires on Si (111) substrates with gassource molecular beam epitaxy (MBE), and the wires were well separated, 50-250 nm in diameter and grew to lengths ranging from 2 µm to 7 µm.
Abstract: We have grown GaN and AlGaN nanowires on Si (111) substrates with gassource molecular beam epitaxy (MBE). No metal catalysts were used. The nanowires displayed a number of interesting materials properties, including room-temperature luminescence intensity greater than that of free-standing HVPE-grown GaN, relaxed lattice parameters, and the tendency of nanowires dispersed in solvents to align in response to electric fields. The wires were well separated, 50–250 nm in diameter, and grew to lengths ranging from 2 µm to 7 µm. Transmission electron microscopy indicated that the wires were free of defects, unlike the surrounding matrix layer.
TL;DR: In this article, a method for the growth of GaN bulk crystals under ammonothermal conditions is described, using polycrystalline GaN as nutrient and hydride vapor phase epitaxy GaN templates as seeds.
TL;DR: It is demonstrated that the activation energy for self-diffusion over the nitrogen sublattice is lower than over the gallium one for all Fermi-level positions, which implies the nitrogen vacancies are major defects in samples annealed at high temperatures.
Abstract: We present results of ab initio calculations for vacancies and divacancies in GaN. Particular attention is paid to nitrogen vacancies and mixed Ga-N divacancies in negatively charged states, which in n-type GaN are found to be energetically comparable with gallium vacancies. We also demonstrate that the activation energy for self-diffusion over the nitrogen sublattice is lower than over the gallium one for all Fermi-level positions, which implies the nitrogen vacancies are major defects in samples annealed at high temperatures. Possibilities for direct observations of nitrogen vacancies through positron annihilation experiments are discussed.
Book•
24 Feb 2006
TL;DR: Advanced Processing of GaN for Electronic Devices Dry Etching of GaNs and Related Materials Design and Fabrication of GAN High Power Rectifiers Chemical, Gas, Biological and Pressure Sensing Nitride-Based Spintronics Novel Insulators for GaN MOSFETs and AlGaN/GaN HEMTs as discussed by the authors.
Abstract: Advanced Processing of GaN for Electronic Devices Dry Etching of GaN and Related Materials Design and Fabrication of GaN High Power Rectifiers Chemical, Gas, Biological and Pressure Sensing Nitride-Based Spintronics Novel Insulators for GaN MOSFETs and AlGaN/GaN MOS-HEMTs
TL;DR: In this article, the effect of crystalline quality on the absorption saturation characteristics was examined and reduction of edge dislocations was found to be a crucial factor in decreasing operation energy.
Abstract: Intersubband transition (ISBT) in GaN quantum wells (QWs) was investigated from the viewpoint of application to ultrafast all-optical switches. The effect of crystalline quality on the absorption saturation characteristics was examined and reduction of edge dislocations was found to be a crucial factor in decreasing operation energy. Then, the switching performance was investigated for devices with improved crystalline quality. Modulation of signal pulses with a pulse interval of less than 1 ps was confirmed. Another device displayed gate-switch operation with an extinction ratio of greater than 10 dB. Comparison of the absorption recovery process in both devices suggested that the process is strongly affected by the QW structure
TL;DR: In this paper, the main reviewed routes are: (i) the high pressure nitrogen solution growth (HP.N.G.), (ii) the Na flux method, and (iii) the ammonothermal crystal growth.
Abstract: Optoelectrical and microelectronic devices involving gallium nitride have become a challenge but their development is limited because of a lack of suitable substrates. This paper deals with the crystal growth of gallium nitride, the processes leading to GaN bulk crystals being significantly expanded during the last decade (the ones involving GaN thin films or nanocrystallites are not studied in this review). The main reviewed routes are: (i) the high pressure nitrogen solution growth (H.P.N.S.G.), (ii) the Na flux method, and (iii) the ammonothermal crystal growth.
TL;DR: In this article, the bottom side of a sapphire substrate was patterned using a dry etching process to increase the light-extraction efficiency of the flip-chip light-emitting diode (FCLED) with a textured substrate.
Abstract: A high light-extraction efficiency was demonstrated in the flip-chip light-emitting diode (FCLED) with a textured sapphire substrate. The bottom side of a sapphire substrate was patterned using a dry etching process to increase the light-extraction efficiency. Light output power measurements indicated that the scattering of photons emitted in the active layer was considerably enhanced at the textured sapphire substrate resulting in an increase in the probability of escaping from the FCLED. The light-output power of the FCLED was increased by 40.2% for a 0.4-mum deep FCLED with a periodic distance of 13-mum mesh-type texture on the bottom side of the sapphire substrate
Patent•
30 Oct 2006TL;DR: In this article, a substrate for epitaxial growth of nitride semiconductor layers is proposed, which is suitable for use in optoelectronics for manufacturing opto-electronic semiconductor devices based on nitrides, in particular for manufacturing semiconductor laser diodes and laser devices.
Abstract: The invention relates to a substrate for epitaxy, especially for preparation of nitride semiconductor layers. Invention covers a bulk nitride mono-crystal characterized in that it is a mono-crystal of gallium nitride and its cross-section in a plane perpendicular to c-axis of hexagonal lattice of gallium nitride has a surface area greater than 100 mm 2 , it is more than 1.0 μm thick and its C-plane surface dislocation density is less than 10 6 /cm 2 , while its volume is sufficient to produce at least one further-processable non-polar A-plane or M-plane plate having a surface area at least 100 mm 2 . More generally, the present invention covers a bulk nitride mono-crystal which is characterized in that it is a mono-crystal of gallium-containing nitride and its cross-section in a plane perpendicular to c-axis of hexagonal lattice of gallium-containing nitride has a surface area greater than 100 mm 2 , it is more 1.0 μm thick and its surface dislocation density is less than 10 6 /cm 2 . Mono-crystals according to the present invention are suitable for epitaxial growth of nitride semiconductor layers. Due to their good crystalline quality they are suitable for use in opto-electronics for manufacturing opto-electronic semiconductor devices based on nitrides, in particular for manufacturing semiconductor laser diodes and laser devices. The a.m bulk mono-crystals of gallium-containing nitride are crystallized on seed crystals. Various seed crystals may be used. The bulk mono-crystals of gallium-containing nitride are crystallized by a method involving dissolution of a gallium-containing feedstock in a supercritical solvent and crystallization of a gallium nitride on a surface of seed crystal, at temperature higher and/or pressure lower than in the dissolution process.
TL;DR: In this paper, an overview of GaN gas-phase and surface-phase chemistry is used to generate a comprehensive model for epitaxial GaN growth from the commonly used precursors, trimethylgallium ((CH 3 ) 3 Ga) and ammonia (NH 3 ).
TL;DR: In this article, the aging process in InGaN laser diodes fabricated by metal organic vapor phase epitaxy on low-dislocation-density, high-pressure-grown bulk gallium nitride crystals was investigated.
Abstract: We have investigated the aging processes in InGaN laser diodes fabricated by metal organic vapor phase epitaxy on low-dislocation-density, high-pressure-grown bulk gallium nitride crystals. The measured threshold current turned out to be a square root function of aging time, indicating the importance of diffusion for device degradation. The differential efficiency, in contrast, was roughly constant during these experiments. From these two observations we can conclude that the main reason for degradation is the diffusion-enhanced increase of nonradiative recombination within the active layer of the laser diode. Additionally, microscopic studies of the degraded structures did not reveal any new dislocations within the active area of the aged diodes, thus identifying point defects as a source of nonradiative processes.
TL;DR: In this paper, the authors report the growth of highly reflective distributed Bragg reflectors (DBRs) in the UV region using the Al0.85In0.15N∕Al0.2Ga0.8N lattice-matched system.
Abstract: We report the growth of highly reflective distributed Bragg reflectors (DBRs) in the UV region using the Al0.85In0.15N∕Al0.2Ga0.8N lattice-matched system. The DBRs were deposited on nearly strain-free Al0.2Ga0.8N templates to avoid strain-induced structural degradations. The appearance of cracks was then completely suppressed. The DBRs exhibit a reflectivity higher than 99% at a wavelength as short as ∼340nm and a stop band width of 215meV (20nm).
TL;DR: In this paper, the growth of high quality aluminum nitride epilayers on large area (6in. diameter) silicon (111) substrates by metal organic chemical vapor deposition was reported.
Abstract: We report on the growth of high quality aluminum nitride (AlN) and gallium nitride (GaN) epilayers on large area (6in. diameter) silicon (111) substrates by metal organic chemical vapor deposition. We have demonstrated the feasibility of growing crack-free high quality III-nitride photonic structures and devices on 6inch Si substrates through the fabrication of blue light emitting diodes based upon nitride multiple quantum wells with high performance. The demonstration further enhances the prospects for achieving photonic integrated circuits based upon nitride-on-Si material system.
TL;DR: A simple and effective ac and dc dielectrophoresis method that can be used to align and manipulate semiconductor gallium nitride (GaN) nanowires (NWs) with variations in the type of electrical fields as well as variations of frequency is reported on.
Abstract: We report on a simple and effective ac and dc dielectrophoresis (DEP) method that can be used to align and manipulate semiconductor gallium nitride (GaN) nanowires (NWs) with variations in the type of electrical fields as well as variations of frequency. We observed that the ability of the alignment and the formation of the assembling nanowires (single or a bundle configuration) strongly depend on the magnitude of both the ac and dc electric fields. The yield results indicate that the GaN NWs, using ac DEP, are better aligned with a higher yield rate of approximately 80% over the entire array in the chip than by using dc DEP. In addition, we first demonstrated the simple hybrid p-n junction structures assembled by n-type GaN nanowires together with a p-type silicon substrate (n-GaN NW/p-Si substrate) using dielectrophoresis. From the transport measurements, the p-n junction structures show well-defined current rectifying behaviour with a low reverse leakage current of approximately 3 x 10(-4) A at -25 V. We believe that our unique p-n junction structures can be useful for electronic and optoelectronic nanodevices such as rectifiers and UV nano-LEDs.