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Journal ArticleDOI

Effect of N/Ga flux ratio on transport behavior of Pt/GaN Schottky diodes

16 Sep 2011-Journal of Applied Physics (American Institute of Physics)-Vol. 110, Iss: 6, pp 064502
TL;DR: In this article, the effect of N/Ga flux ratio on structural, morphological, and optical properties of GaN films on c-plane sapphire by plasma-assisted molecular beam epitaxy (PAMBE) was studied.
Abstract: GaN films were grown on c-plane sapphire by plasma-assisted molecular beam epitaxy (PAMBE). The effect of N/Ga flux ratio on structural, morphological, and optical properties was studied. The dislocation density found to increase with increasing the N/Ga ratio. The surface morphology of the films as seen by scanning electron microscopy shows pits on the surface and found that the pit density on the surface increases with N/Ga ratio. The room temperature photoluminescence study reveals the shift in band-edge emission toward the lower energy with increase in N/Ga ratio. This is believed to arise from the reduction in compressive stress in the films as is evidenced by room temperature Raman study. The transport studied on the Pt/GaN Schottky diodes showed a significant increase in leakage current with an increase in N/Ga ratio and was found to be caused by the increase in pit density as well as increase in dislocation density in the GaN films.
Citations
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Journal ArticleDOI
TL;DR: In this article, the authors have grown InGaN/GaN heterostructures using plasma-assisted molecular beam epitaxy and studied the temperature dependent electrical transport characteristics, where the barrier height and the ideally factor were found to be temperature dependent.
Abstract: We have grown InGaN/GaN heterostructures using plasma-assisted molecular beam epitaxy and studied the temperature dependent electrical transport characteristics. The barrier height (φb) and the ideally factor (η) estimated using thermionic emission model were found to be temperature dependent. The conventional Richardson plot of ln(Js/T2) versus 1/kT showed two temperature regions (region-I: 400–500 K and region-II: 200–350 K) and it provides Richardson constants (A∗) which are much lower than the theoretical value of GaN. The observed variation in the barrier height and the presence of two temperature regions were attributed to spatial barrier inhomogeneities at the heterojunction interface and was explained by assuming a double Gaussian distribution of barrier heights with mean barrier height values 1.61 and 1.21 eV with standard deviation (σs2) of 0.044 and 0.022 V, respectively. The modified Richardson plot of ln(Js/T2) − (q2σs2/2k2T2) versus 1/kT for two temperature regions gave mean barrier height v...

18 citations

Journal ArticleDOI
TL;DR: In this article, a-plane GaN thin films are grown on r-plane sapphire using three different growth approaches by plasma-assisted molecular beam epitaxy (PAMBE) and in situ reflection high-energy electron diffraction (RHEED) analysis is performed during and after the growth to monitor the growth mode.
Abstract: Present work focuses on improving the quality of nonpolar a-plane GaN thin films by introducing unconventional new efficient growth conditions without compromising their UV photodetection properties. These epitaxial thin films are grown on r-plane sapphire using three different growth approaches by plasma-assisted molecular beam epitaxy (PAMBE). In situ reflection high-energy electron diffraction (RHEED) analysis is performed during and after the growth to monitor the growth mode, and it is found that the films assumed desired 2D mode during the growth. The crystalline quality and the phase purity of the films are assessed with the help of high-resolution X-ray diffraction and Raman spectroscopy. All the films are found to contain compressive stress, which indicate that all the films are strained and epitaxial. The temporal response is carried out in all the three batches, which is very stable. Sensitivity, responsivity, transit time, and gain values are estimated. Highest responsivity and the corresponding gain are found to be around 25 AW(-1), 86.47 at 1 V bias, respectively. These are the highest reported values so far for a-plane GaN at such low voltages.

16 citations

Journal ArticleDOI
TL;DR: In this article, the growth of pure gallium nitride (GaN) nanostructures on different silicon (Si) substrates by thermal vapor deposition via the direct reaction of gallium with volatile ammonia solution is reported.
Abstract: We report on the growth of highly pure and single crystalline gallium nitride (GaN) nanostructures on different silicon (Si) substrates by thermal vapor deposition via the direct reaction of gallium with volatile ammonia solution. The structural and optical characteristics of the as-grown GaN/Si nanostructured heterojunctions are investigated. The morphology of the formed GaN nanostructures is strongly dependent on the crystal orientation of the Si substrate. The X-ray diffraction and Raman analysis reveal that the fabricated GaN nanostructures have a hexagonal wurtzite structure. The photoluminescence spectra of all GaN nanostructures exhibit a strong near-band-edge ultraviolet (UV) emission peak (365–372 nm), which illustrates their potential in optoelectronic applications. The current–voltage measurements under dark, visible, and UV illumination conditions are performed to study the light sensing ability of the fabricated heterojunctions. Under reverse bias (5 V), the photocurrent of the GaN/n-Si (111) photodetector was comparably much higher than that of the GaN/n-Si (100) photodetector, probably due to the better quality of the GaN formed on Si (111) compared with those formed on Si (100), resulting in a higher photoresponse. The calculated rectification ratio revealed that the sensitivity of the GaN/n-Si (111) photodiode is higher than that of the GaN/n-Si (100), indicating the importance of the interface architecture. The fabricated photodiodes showed photoresponse toward UV and visible wavelengths, demonstrating shorter rise and decay times compared with other materials used to fabricate UV and visible light photodetectors. The prototype device shows a simple method for GaN synthesis and demonstrates the possibility of constructing nanoscale photodetectors for nano-optics applications.

13 citations

Journal ArticleDOI
TL;DR: In this paper, a single-phase InGaN epitaxial films were grown on GaN template by plasma-assisted molecular beam epitaxy and the composition of indium incorporation was found to be 23%.

8 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a detailed report on the modulation in the electrical properties of VO2/Si heterostructures by application of an external electrical field across VO2 thin films.
Abstract: Smart multifunctional materials such as vanadium dioxide (VO2), which exhibit a reversible semiconductor-to-metal transition (SMT), provide a new route toward engineering high speed switchable devices. Here, we present a detailed report on the modulation in the electrical properties of VO2/Si heterostructures by application of an external electrical field across VO2 thin films. Single-phase VO2 thin films have been deposited on an Si(111) substrate using the pulsed laser deposition technique. The electrical transport behavior across the VO2/Si heterostructure has been studied in the temperature range of 35–105 °C, and a reversible SMT can be seen at 68 and 63 °C for heating and cooling cycles, respectively. The temperature-dependent resistance of the device shows a hysteresis loop around the transition temperature of the VO2 thin film. In addition, the device shows a significant change in junction current when an external bias is applied on the VO2 thin film, and this phenomenon has been utilized to study the switching behavior of the device. Such behavior is due to the change in interfacial barrier height because of the bias dependent tilting of electronic energy bands of the VO2 thin film. Our results offer novel opportunities to externally control the electrical transport of vertical heterostructures and can be beneficial for extending the notion of electrical field modulation in electrical switches and sensors.

6 citations

References
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Book
01 Jan 1969
TL;DR: In this article, the authors present a review of the properties of Semiconductors and their properties in terms of physics and properties of devices, including the following: 1.1 Introduction. 1.2 Crystal Structure.
Abstract: Introduction. Part I Semiconductor Physics. Chapter 1 Physics and Properties of Semiconductors-A Review. 1.1 Introduction. 1.2 Crystal Structure. 1.3 Energy Bands and Energy Gap. 1.4 Carrier Concentration at Thermal Equilibrium. 1.5 Carrier-Transport Phenomena. 1.6 Phonon, Optical, and Thermal Properties. 1.7 Heterojunctions and Nanostructures. 1.8 Basic Equations and Examples. Part II Device Building Blocks. Chapter 2 p-n Junctions. 2.1 Introduction. 2.2 Depletion Region. 2.3 Current-Voltage Characteristics. 2.4 Junction Breakdown. 2.5 Transient Behavior and Noise. 2.6 Terminal Functions. 2.7 Heterojunctions. Chapter 3 Metal-Semiconductor Contacts. 3.1 Introduction. 3.2 Formation of Barrier. 3.3 Current Transport Processes. 3.4 Measurement of Barrier Height. 3.5 Device Structures. 3.6 Ohmic Contact. Chapter 4 Metal-Insulator-Semiconductor Capacitors. 4.1 Introduction. 4.2 Ideal MIS Capacitor. 4.3 Silicon MOS Capacitor. Part III Transistors. Chapter 5 Bipolar Transistors. 5.1 Introduction. 5.2 Static Characteristics. 5.3 Microwave Characteristics. 5.4 Related Device Structures. 5.5 Heterojunction Bipolar Transistor. Chapter 6 MOSFETs. 6.1 Introduction. 6.2 Basic Device Characteristics. 6.3 Nonuniform Doping and Buried-Channel Device. 6.4 Device Scaling and Short-Channel Effects. 6.5 MOSFET Structures. 6.6 Circuit Applications. 6.7 Nonvolatile Memory Devices. 6.8 Single-Electron Transistor. Chapter 7 JFETs, MESFETs, and MODFETs. 7.1 Introduction. 7.2 JFET and MESFET. 7.3 MODFET. Part IV Negative-Resistance and Power Devices. Chapter 8 Tunnel Devices. 8.1 Introduction. 8.2 Tunnel Diode. 8.3 Related Tunnel Devices. 8.4 Resonant-Tunneling Diode. Chapter 9 IMPATT Diodes. 9.1 Introduction. 9.2 Static Characteristics. 9.3 Dynamic Characteristics. 9.4 Power and Efficiency. 9.5 Noise Behavior. 9.6 Device Design and Performance. 9.7 BARITT Diode. 9.8 TUNNETT Diode. Chapter 10 Transferred-Electron and Real-Space-Transfer Devices. 10.1 Introduction. 10.2 Transferred-Electron Device. 10.3 Real-Space-Transfer Devices. Chapter 11 Thyristors and Power Devices. 11.1 Introduction. 11.2 Thyristor Characteristics. 1 1.3 Thyristor Variations. 11.4 Other Power Devices. Part V Photonic Devices and Sensors. Chapter 12 LEDs and Lasers. 12.1 Introduction. 12.2 Radiative Transitions. 12.3 Light-Emitting Diode (LED). 12.4 Laser Physics. 12.5 Laser Operating Characteristics. 12.6 Specialty Lasers. Chapter 13 Photodetectors and Solar Cells. 13.1 Introduction. 13.2 Photoconductor. 13.3 Photodiodes. 13.4 Avalanche Photodiode. 13.5 Phototransistor. 13.6 Charge-Coupled Device (CCD). 13.7 Metal-Semiconductor-Metal Photodetector. 13.8 Quantum-Well Infrared Photodetector. 13.9 Solar Cell. Chapter 14 Sensors. 14.1 Introduction. 14.2 Thermal Sensors. 14.3 Mechanical Sensors. 14.4 Magnetic Sensors. 14.5 Chemical Sensors. Appendixes. A. List of Symbols. B. International System of Units. C. Unit Prefixes. D. Greek Alphabet. E. Physical Constants. F. Properties of Important Semiconductors. G. Properties of Si and GaAs. H. Properties of SiO, and Si3N. Index.

487 citations

Journal ArticleDOI
TL;DR: The surface morphologies of GaN grown by plasma-assisted molecular beam epitaxy under various growth conditions have been investigated in this article, where three growth regimes (one N stable and two Ga stable) are identified on a surface structure diagram (Ga/N ratio versus substrate temperature).
Abstract: The characteristic surface morphologies of GaN grown by plasma-assisted molecular beam epitaxy under various growth conditions have been investigated. Three growth regimes (one N stable and two Ga stable) are identified on a surface structure diagram (Ga/N ratio versus substrate temperature). The boundary between the N-stable regime (low Ga/N ratios) and the two Ga-stable regimes (high Ga/N ratios) is determined by the growth rate of the films and is constant over the range of substrate temperatures investigated. The boundary between the two Ga-stable regimes (the Ga-droplet regime and the intermediate regime) is determined by the formation of Ga droplets and has an Arrhenius dependence with substrate temperature. The characteristic morphologies of films grown within each of these regimes are investigated using atomic force microscopy and transmission electron microscopy. N-stable films have rough, heavily pitted morphologies. Films grown within the intermediate phase have areas of flat surface between la...

470 citations

Journal ArticleDOI
TL;DR: In this article, the structure, morphology, and optical properties of homoepitaxial GaN layers grown by molecular beam epitaxy on metalorganic chemical vapor deposition (MOCVD)-grown GaN “template” layers were investigated as a function of the group III/group V flux ratio during growth.
Abstract: The structure, morphology, and optical properties of homoepitaxial GaN layers grown by molecular beam epitaxy on metalorganic chemical vapor deposition (MOCVD)-grown GaN “template” layers were investigated as a function of the group III/group V flux ratio during growth GaN layers grown with a low III/V ratio (N-stable growth) displayed a faceted surface morphology and a tilted columnar structure with a high density of stacking faults In contrast, films grown with a high III/V ratio (Ga-stable growth) displayed comparable structure to the underlying MOCVD-grown template The transition from N-stable to Ga-stable growth modes was found to occur over a narrow range of Ga fluxes at a growth temperature of 650 °C Evidence of Ga accumulation and step-flow growth was observed for films grown under Ga-stable conditions, leading to the formation of spiral growth features at the surface termination of mixed edge/screw dislocations Photoluminescence measurements indicate that the deep-level (∼550 nm) emission is

378 citations

Journal ArticleDOI
TL;DR: In this paper, a combination of in situ reflection high-energy electron diffraction, double-crystal x-ray diffraction and cross-sectional transmission electron microscopy was used to determine the film/substrate epitaxial relationships.
Abstract: Reactive‐ion molecular‐beam epitaxy has been used to grow epitaxial hexagonal‐structure α‐GaN on Al2O3(0001) and Al2O3(0112) substrates and metastable zinc‐blende‐structure β‐GaN on MgO(001) under the following conditions: growth temperature Ts=450–800 °C; incident N+2/Ga flux ratio JN+2/JGa=1–5; and N+2 kinetic energy EN+2=35–90 eV The surface structure of the α‐GaN films was (1×1), with an ≊3% contraction in the in‐plane lattice constant for films grown on Al2O3(0001), while the β‐GaN films exhibited a 90°‐rotated two‐domain (4×1) reconstruction Using a combination of in situ reflection high‐energy electron diffraction, double‐crystal x‐ray diffraction, and cross‐sectional transmission electron microscopy, the film/substrate epitaxial relationships were determined to be: (0001)GaN∥ (0001)Al2O3 with [2110]GaN∥[1100]Al2O3 and [1100]GaN∥[1210]Al2O3, (2110)GaN∥(0112)Al2O3 with [0001]GaN∥[0111]Al2O3 and [0110]GaN∥[2110]Al2O3, and (001)GaN∥(001)MgO with [001]GaN∥[001]MgOFilms with the lowest e

373 citations

Journal ArticleDOI
TL;DR: In this paper, the defects which penetrate the GaN films are predominantly perfect edge dislocations with Burgers vectors of the 1/3-1120-type, lying along the [0001] growth direction.
Abstract: Microstructure of α‐GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AlN (or GaN) buffer layers has been studied by transmission electron microscopy. The defects which penetrate the GaN films are predominantly perfect edge dislocations with Burgers vectors of the 1/3〈1120〉 type, lying along the [0001] growth direction. The main sources of threading dislocations are the low angle grain boundaries, formed during coalescence of islands at the initial stages of GaN growth. The grain sizes range from 50 to 500 nm, with in‐plane misorientations of less than 3°. The nature of these threading dislocations suggests that the defect density would not likely decrease appreciably at increasing film thickness, and the suppression of these dislocations could be more difficult.

274 citations