Physica. E, Low-Dimensional systems and nanostructures, 2004
We present the effect of all standard scattering mechanisms, including scattering by acoustic and... more We present the effect of all standard scattering mechanisms, including scattering by acoustic and optical phonons, remote and background impurities and dislocation, on two-dimensional electron gas (2DEG) transport in AlGaN/GaN modulation doped-heterostructures. The most important scattering mechanisms limiting electron transport are identified. From the calculated dependence of mobility on temperature, it is clear that dislocation scattering dominates the low temperature mobility of twodimensional (2D) electrons in GaN/AlGaN structures with a high electron density n s >10 12 cm-2 and the maximum 2DEG mobilities will be in the 10 2-10 4 cm 2 /V.s range for dislocation density of 4x10 10 cm-2 and carrier densities in the 1x10 12-2x10 13 cm-2. This theoretical calculations are fairly agree with the same mobility value obtained by the experimental for 4x10 10 cm-2 dislocation density. The results are compared to the transport to quantum lifetime ratios due to charge dislocations. We find that the ratio is larger for dislocation scattering than for impurity scattering.
The results of experimental and theoretical studies concerning the temperature dependence of elec... more The results of experimental and theoretical studies concerning the temperature dependence of electron mobility in a two-dimensional electron gas (2DEG) confined near the interface of an AlGaN/GaN heterostructure are presented. In order to compare the experimental results with the theory a simple analytical formula is used for the low-field electron mobility, which uses the 2D degenerate statistics for a 2DEG confined in a triangular well. All standard scattering mechanisms, including scattering by acoustic and optical phonons, remote and background impurities and interface roughness (IFR), have been included in the calculations. From the calculated dependence of mobility on temperature, it is clear that IFR and ionised impurity scattering dominate the low-temperature mobility of 2D electrons in AlGaN/GaN structures with a high electron density n s > 10 12 cm-2. At intermediate temperatures, acoustic deformation potential and piezoelectric scattering are the dominant mechanisms. The polar optical phonon scattering is found to be the important mechanism of scattering at high temperatures. The experimental results are discussed in the light of the calculated mobility.
In this study, the Hall effect measurement of graphene on SiC substrate was carried out as a func... more In this study, the Hall effect measurement of graphene on SiC substrate was carried out as a function of temperature (12300 K). Hall data were first analyzed to extract the temperature dependent mobilities and carrier densities of the bulk (3D) and two dimensional (2D) channels using a Simple Parallel Conduction Extraction Method (SPCEM) successfully. High carrier mobility 2.296 cm 2 /V.s from the graphene layer and low carrier mobility 813 cm 2 /V.s from the SiC were obtained at room temperature. By using SPCEM extracted data, 3D and 2D scattering mechanisms were analyzed and the dominant scattering mechanisms in low and high temperature regimes were determined. It was found that the transport was mainly determined by scattering processes in 2D graphene.
The effect of hot phonons on the drift velocity in GaN/AlGaN two dimensional electron gas
Physica E-low-dimensional Systems & Nanostructures, 2004
We present the effect of hot-phonon production on the high-field drift velocity in the steady sta... more We present the effect of hot-phonon production on the high-field drift velocity in the steady state in GaN/AlGaN heterostructures. The results are compared with a model taking into account the effect of hot phonon production on the high-field transport of electrons. Experimental results show that the drift velocity saturates at around v d ≈3.8×10 5 cm / s at an electric field of F≈8.9×10 2 V / cm at 3.8 K . The theoretical calculations show that the enhancement of the momentum relaxation rate due to the production of non-drifting hot phonons reduces the drift velocity at high field. The reduction in the drift velocity increases with increasing population of non-drifting non-equilibrium phonons (LO phonons).
Physica E Low Dimensional Systems and Nanostructures, Jun 1, 2004
We present the effect of all standard scattering mechanisms, including scattering by acoustic and... more We present the effect of all standard scattering mechanisms, including scattering by acoustic and optical phonons, remote and background impurities and dislocation, on two-dimensional electron gas (2DEG) transport in AlGaN/GaN modulation doped-heterostructures. The most important scattering mechanisms limiting electron transport are identified. From the calculated dependence of mobility on temperature, it is clear that dislocation scattering dominates the low temperature mobility of twodimensional (2D) electrons in GaN/AlGaN structures with a high electron density n s >10 12 cm-2 and the maximum 2DEG mobilities will be in the 10 2-10 4 cm 2 /V.s range for dislocation density of 4x10 10 cm-2 and carrier densities in the 1x10 12-2x10 13 cm-2. This theoretical calculations are fairly agree with the same mobility value obtained by the experimental for 4x10 10 cm-2 dislocation density. The results are compared to the transport to quantum lifetime ratios due to charge dislocations. We find that the ratio is larger for dislocation scattering than for impurity scattering.
Current-transport mechanisms were investigated in Schottky contacts on AlInN/AlN/GaN single chann... more Current-transport mechanisms were investigated in Schottky contacts on AlInN/AlN/GaN single channel (SC) and AlInN/AlN/GaN/AlN/GaN double channel (DC) heterostructures. A simple model was adapted to the current-transport mechanisms in DC heterostructure. In this model, two Schottky diodes are in series: one is a metal-semiconductor barrier layer (AIInN) Schottky diode and the other is an equivalent Schottky diode, which is due to the heterojunction between the AlN and GaN layer. Capacitance-voltage studies show the formation of a two-dimensional electron gas at the AlN/GaN interface in the SC and the first AlN/GaN interface from the substrate direction in the DC. In order to determine the current mechanisms for SC and DC heterostructures, we fit the analytical expressions given for the tunneling current to the experimental current-voltage data over a wide range of applied biases as well as at different temperatures. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. At both a low and medium forward-bias voltage values for Schottky contacts on AlInN/ AlN/GaN/AlN/GaN DC and AlInN/AlN/GaN SC heterostructures, the data are consistent with electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-420 K.
Physica E: Low-dimensional Systems and Nanostructures, 2004
The in uence of interface roughness on the mobility of two-dimensional electrons in GaN/AlGaN HEM... more The in uence of interface roughness on the mobility of two-dimensional electrons in GaN/AlGaN HEMT structures are theoretically investigated in light of the measured mobility. Experimental mobility of 2912 cm 2 =V s at 4:2 K, remains almost constant up to lattice temperature TL = 150 K. It then decreases rapidly down to 1067 cm 2 =V s at TL = 300 K. In order to compare the experimental results with the theory we use a simple analytical formula for low-ÿeld electron mobility that uses the two-dimensional degenerate statistics for a 2DEG conÿned in a triangular well. Interface-roughness scattering dominates the low-temperature mobility of two-dimensional electrons in GaN/AlGaN structures with a high electron density ns ¿ 10 12 cm −2. From comparison between theory and experiment, the correlation length () and lateral size () of roughness for GaN /AlGaN 2DEG are estimated. The e ect of phonons scattering from interface roughness and well-width uctuations on low-ÿeld mobility of 2DEG in GaN/AlGaN is also investigated.
Physica. E, Low-Dimensional systems and nanostructures, 2004
We present the effect of all standard scattering mechanisms, including scattering by acoustic and... more We present the effect of all standard scattering mechanisms, including scattering by acoustic and optical phonons, remote and background impurities and dislocation, on two-dimensional electron gas (2DEG) transport in AlGaN/GaN modulation doped-heterostructures. The most important scattering mechanisms limiting electron transport are identified. From the calculated dependence of mobility on temperature, it is clear that dislocation scattering dominates the low temperature mobility of twodimensional (2D) electrons in GaN/AlGaN structures with a high electron density n s >10 12 cm-2 and the maximum 2DEG mobilities will be in the 10 2-10 4 cm 2 /V.s range for dislocation density of 4x10 10 cm-2 and carrier densities in the 1x10 12-2x10 13 cm-2. This theoretical calculations are fairly agree with the same mobility value obtained by the experimental for 4x10 10 cm-2 dislocation density. The results are compared to the transport to quantum lifetime ratios due to charge dislocations. We find that the ratio is larger for dislocation scattering than for impurity scattering.
The results of experimental and theoretical studies concerning the temperature dependence of elec... more The results of experimental and theoretical studies concerning the temperature dependence of electron mobility in a two-dimensional electron gas (2DEG) confined near the interface of an AlGaN/GaN heterostructure are presented. In order to compare the experimental results with the theory a simple analytical formula is used for the low-field electron mobility, which uses the 2D degenerate statistics for a 2DEG confined in a triangular well. All standard scattering mechanisms, including scattering by acoustic and optical phonons, remote and background impurities and interface roughness (IFR), have been included in the calculations. From the calculated dependence of mobility on temperature, it is clear that IFR and ionised impurity scattering dominate the low-temperature mobility of 2D electrons in AlGaN/GaN structures with a high electron density n s > 10 12 cm-2. At intermediate temperatures, acoustic deformation potential and piezoelectric scattering are the dominant mechanisms. The polar optical phonon scattering is found to be the important mechanism of scattering at high temperatures. The experimental results are discussed in the light of the calculated mobility.
In this study, the Hall effect measurement of graphene on SiC substrate was carried out as a func... more In this study, the Hall effect measurement of graphene on SiC substrate was carried out as a function of temperature (12300 K). Hall data were first analyzed to extract the temperature dependent mobilities and carrier densities of the bulk (3D) and two dimensional (2D) channels using a Simple Parallel Conduction Extraction Method (SPCEM) successfully. High carrier mobility 2.296 cm 2 /V.s from the graphene layer and low carrier mobility 813 cm 2 /V.s from the SiC were obtained at room temperature. By using SPCEM extracted data, 3D and 2D scattering mechanisms were analyzed and the dominant scattering mechanisms in low and high temperature regimes were determined. It was found that the transport was mainly determined by scattering processes in 2D graphene.
The effect of hot phonons on the drift velocity in GaN/AlGaN two dimensional electron gas
Physica E-low-dimensional Systems & Nanostructures, 2004
We present the effect of hot-phonon production on the high-field drift velocity in the steady sta... more We present the effect of hot-phonon production on the high-field drift velocity in the steady state in GaN/AlGaN heterostructures. The results are compared with a model taking into account the effect of hot phonon production on the high-field transport of electrons. Experimental results show that the drift velocity saturates at around v d ≈3.8×10 5 cm / s at an electric field of F≈8.9×10 2 V / cm at 3.8 K . The theoretical calculations show that the enhancement of the momentum relaxation rate due to the production of non-drifting hot phonons reduces the drift velocity at high field. The reduction in the drift velocity increases with increasing population of non-drifting non-equilibrium phonons (LO phonons).
Physica E Low Dimensional Systems and Nanostructures, Jun 1, 2004
We present the effect of all standard scattering mechanisms, including scattering by acoustic and... more We present the effect of all standard scattering mechanisms, including scattering by acoustic and optical phonons, remote and background impurities and dislocation, on two-dimensional electron gas (2DEG) transport in AlGaN/GaN modulation doped-heterostructures. The most important scattering mechanisms limiting electron transport are identified. From the calculated dependence of mobility on temperature, it is clear that dislocation scattering dominates the low temperature mobility of twodimensional (2D) electrons in GaN/AlGaN structures with a high electron density n s >10 12 cm-2 and the maximum 2DEG mobilities will be in the 10 2-10 4 cm 2 /V.s range for dislocation density of 4x10 10 cm-2 and carrier densities in the 1x10 12-2x10 13 cm-2. This theoretical calculations are fairly agree with the same mobility value obtained by the experimental for 4x10 10 cm-2 dislocation density. The results are compared to the transport to quantum lifetime ratios due to charge dislocations. We find that the ratio is larger for dislocation scattering than for impurity scattering.
Current-transport mechanisms were investigated in Schottky contacts on AlInN/AlN/GaN single chann... more Current-transport mechanisms were investigated in Schottky contacts on AlInN/AlN/GaN single channel (SC) and AlInN/AlN/GaN/AlN/GaN double channel (DC) heterostructures. A simple model was adapted to the current-transport mechanisms in DC heterostructure. In this model, two Schottky diodes are in series: one is a metal-semiconductor barrier layer (AIInN) Schottky diode and the other is an equivalent Schottky diode, which is due to the heterojunction between the AlN and GaN layer. Capacitance-voltage studies show the formation of a two-dimensional electron gas at the AlN/GaN interface in the SC and the first AlN/GaN interface from the substrate direction in the DC. In order to determine the current mechanisms for SC and DC heterostructures, we fit the analytical expressions given for the tunneling current to the experimental current-voltage data over a wide range of applied biases as well as at different temperatures. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. At both a low and medium forward-bias voltage values for Schottky contacts on AlInN/ AlN/GaN/AlN/GaN DC and AlInN/AlN/GaN SC heterostructures, the data are consistent with electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-420 K.
Physica E: Low-dimensional Systems and Nanostructures, 2004
The in uence of interface roughness on the mobility of two-dimensional electrons in GaN/AlGaN HEM... more The in uence of interface roughness on the mobility of two-dimensional electrons in GaN/AlGaN HEMT structures are theoretically investigated in light of the measured mobility. Experimental mobility of 2912 cm 2 =V s at 4:2 K, remains almost constant up to lattice temperature TL = 150 K. It then decreases rapidly down to 1067 cm 2 =V s at TL = 300 K. In order to compare the experimental results with the theory we use a simple analytical formula for low-ÿeld electron mobility that uses the two-dimensional degenerate statistics for a 2DEG conÿned in a triangular well. Interface-roughness scattering dominates the low-temperature mobility of two-dimensional electrons in GaN/AlGaN structures with a high electron density ns ¿ 10 12 cm −2. From comparison between theory and experiment, the correlation length () and lateral size () of roughness for GaN /AlGaN 2DEG are estimated. The e ect of phonons scattering from interface roughness and well-width uctuations on low-ÿeld mobility of 2DEG in GaN/AlGaN is also investigated.
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