Effect of N/Ga flux ratio on transport behavior of Pt/GaN Schottky diodes
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
More filters
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
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
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
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
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
More filters
TL;DR: In this article, the authors measured the curvature of wafer bending to measure the biaxial compressive stress in GaN epitaxial layers with different thicknesses grown on sapphire substrates by metalorganic vapor phase epitaxy using an AlN buffer layer.
Abstract: Thermal stress in GaN epitaxial layers with different thicknesses grown on sapphire substrates by metalorganic vapor phase epitaxy using an AlN buffer layer was investigated. Biaxial compressive stress in the GaN layer, due to the difference in the thermal expansion coefficients between GaN and sapphire, was obtained by measuring the curvature of wafer bending, and the observed stress agreed with the calculated stress. In Raman measurements, the E2 phonon peak of GaN was found to shift and broaden with the stress as a consequence of the change of the elastic constants with strain. The frequency shift Δω (in cm−1) was obtained for the first time, given by the relation: Δω=6.2 σ, where the biaxial stress σ is expressed in GPa.
265 citations
TL;DR: In this article, temperature-dependent current-voltage measurements have been used to determine the reverse-bias leakage current mechanisms in Schottky diodes fabricated on GaN grown by molecular-beam epitaxy.
Abstract: Temperature-dependent current–voltage measurements have been used to determine the reverse-bias leakage current mechanisms in Schottky diodes fabricated on GaN grown by molecular-beam epitaxy, and two dominant mechanisms are clearly identified. The first mechanism is field-emission tunneling from the metal into the semiconductor, which is dominant at low temperatures and which, at higher temperatures, becomes significant for large reverse-bias voltages. The second mechanism, presumed to be associated with dislocation-related leakage current paths, is observed to have an exponential temperature dependence and becomes significant above approximately 275 K. The temperature dependence of the second mechanism is consistent with either one-dimensional variable-range-hopping conduction along the dislocation or trap-assisted tunneling.
260 citations
TL;DR: In this paper, the dc characteristics and microwave performance of AlGaN/GaN heterostructure field effect transistors in the temperature range from 25 to 300°C were investigated.
Abstract: We report on the dc characteristics and microwave performance of AlGaN/GaN heterostructure field effect transistors in the temperature range from 25 to 300 °C. At temperatures above 200 °C, we observe the temperature activated shunt conductance which is independent of the gate voltage (the activation energy is 0.505 eV). The cutoff frequency and the maximum frequency of oscillations vary from 22 and 70 GHz at 25 °C to 5 and 4 GHz at 300 °C, respectively. The gate leakage current in the range of gate biases from −4 to +1 V is small and nearly proportional to the gate voltage even at 300 °C. At temperatures above 200 °C, the gate leakage current is temperature activated (the activation energy is 0.88 eV). These results show that deep traps strongly affect the AlGaN/GaN characteristics at elevated temperatures.
256 citations
TL;DR: In this paper, materials and devices issues are considered to provide a full picture of the advances in nitride UV photodetection, including basic structures like photoconductors, Schottky, p-i-n and metal-semiconductor-metal photodiodes and phototransistors.
Abstract: III nitrides have become the most exciting challenge in optoelectronic materials in the last decade. Their intrinsic properties and an intense technological effort have made possible the fabrication of reliable and versatile detectors for short wavelengths. In this work, materials and devices issues are considered to provide a full picture of the advances in nitride UV photodetection. First, basic structures like photoconductors, Schottky, p-i-n and metal-semiconductor-metal photodiodes and phototransistors are compared, with emphasis on their specific properties and performance limitations. The efforts in the design and fabrication of more advanced detectors, in the search for higher quantum efficiency, contrast, signal-to-noise or speed operation, are reviewed afterwards. Metal-insulator-semiconductor diodes, avalanche photodetectors and GaN array detectors for UV imaging are also described. Further device optimization is linked with present materials issues, mainly due to the nitride quality, which is a direct result of the substrate used. The influence of substrates and dislocations on detector behaviour is discussed in detail. As an example of AlGaN photodetector applications, monitoring of the solar UV-B radiation to prevent erythema and skin cancer is presented.
252 citations
TL;DR: In this paper, the influence of various thicknesses of AlN buffer layers on the strain in thin GaN films was studied by x-ray diffraction and Raman and photoluminescence spectroscopy.
Abstract: The influence of biaxial stress on the optical properties of thin GaN films is studied by x‐ray diffraction and Raman and photoluminescence spectroscopy. The stress is caused by differences in the thermal expansion coefficient and lattice mismatch between the film and c‐plane sapphire substrates. In particular, the influence of various thicknesses of AlN buffer layers on the strain in GaN films is studied. GaN/AlN films were deposited by low pressure metal organic chemical vapor deposition using triethylgallium and tritertbutylaluminum and ammonia. We observe a pronounced reduction of strain in the GaN films with increasing buffer thickness: An AlN buffer layer thicker than 200 nm eliminates the stress completely. Estimates of the linear coefficient for the near band gap luminescence shift due to biaxial compressive strain yield a value of 24 meV/GPa.
207 citations