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1.
宋杰  许福军  黄呈橙  林芳  王新强  杨志坚  沈波 《中国物理 B》2011,20(5):57305-057305
The temperature dependence of carrier transport properties of AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures has been investigated.It is shown that the Hall mobility in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures is higher than that in Al0.25Ga0.75N/GaN heterostructures at temperatures above 500 K,even the mobility in the former is much lower than that in the latter at 300 K.More importantly,the electron sheet density in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures decreases slightly,whereas the electron sheet density in Al0.25Ga0.75N/GaN heterostructures gradually increases with increasing temperature above 500 K.It is believed that an electron depletion layer is formed due to the negative polarization charges at the InyGa1-yN/GaN heterointerface induced by the compressive strain in the InyGa1-yN channel,which e-ectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.  相似文献   

2.
We show that the large band offsets between GaN and InN and the heavy carrier effective masses preclude the use of the virtual crystal approximation to describe the electronic structure of Ga1−xInxN/GaN heterostructures, while this approximation works very well for the Ga1−xInxAs/GaAs heterostructures.  相似文献   

3.
We have performed a first-principle Full Potential Linearized Augmented Plane Waves calculation within the local density approximation (LDA) to the zinc-blende AlxGa1−xAs1−yNy to predict its optical properties as a function of N and Al mole fractions. The accurate calculations of electronic properties such as band structures and optical properties like refractive index, reflectivity and absorption coefficient of AlxGa1−xAs and AlxGa1−xAs1−yNy with x≤0.375 and y up to 4% are presented. AlxGa1−xAs on GaAs have a lattice mismatch less than 0.16% and the lattice constant of AlxGa1−xAs has a derivation parameter of 0.0113±0.0024. The band gap energies are calculated by LDA and the band anticrossing model using a matrix element of CMN=2.32 and a N level of EN=(1.625+0.069x) eV. The results show that AlxGa1−xAs can be very useful as a barrier layer in separate confinement heterostructure lasers and indicate that the best choice of x and y AlxGa1−xAs1−yNy could be an alternative to AlxGa1−xAs when utilized as active layers in quantum well lasers and high-efficiency solar cell structures.  相似文献   

4.
We present numerical optimization of carrier confinement characteristics in (AlxGa1−xN/AlN)SLs/GaN heterostructures in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrödinger, Poisson, potential and charge balance equations. It is found that the sheet carrier density in GaN channel increases nearly linearly with the thickness of AlN although the whole thickness and equivalent Al composition of AlxGa1−xN/AlN superlattices (SLs) barrier are kept constant. This result leads to the carrier confinement capability approaches saturation with thicknesses of AlN greater than 0.6 nm. Furthermore, the influence of carrier concentration distribution on carrier mobility was discussed. Theoretical calculations indicate that the achievement of high sheet carrier density is a trade-off with mobility.  相似文献   

5.
Raman and Fourier transform infrared (FTIR) spectroscopies have been utilized to measure long-wavelength optical lattice vibrations of high-quality quaternary AlxInyGa1−x−yN thin films at room temperature. The AlxInyGa1−x−yN films were grown on c-plane (0 0 0 1) sapphire substrates with AlN as buffer layers using plasma assisted molecular beam epitaxy (PA-MBE) technique with aluminum (Al) mole fraction x ranging from 0.0 to 0.2 and constant indium (In) mole fraction y=0.1. Pseudo unit cell (PUC) model was applied to investigate the phonons frequency, mode number, static dielectric constant, and high frequency dielectric constant of the AlxInyGa1−x−yN mixed crystals. The theoretical results were compared with the experimental results obtained from the quaternary samples by using Raman and FTIR spectroscopies. The experimental results indicated that the AlxInyGa1−x−yN alloy had two-mode behavior, which includes A1(LO), E1(TO), and E2(H). Thus, these results are in agreement with the theoretical results of PUC model, which also revealed a two-mode behavior for the quaternary nitride. We also obtained new values of E1(TO) and E2(H) for the quaternary nitride samples that have not yet been reported in the literature.  相似文献   

6.
Tunneling induced electron transfer in SiNx/Al0.22Ga0.78N/GaN based metal-insulator-semiconductor (MIS) structures has been investigated by means of capacitance-voltage (C-V) measurements at various temperatures. Large clock-wise hysteresis window in C-V profiles indicates the injection of electrons from the two-dimensional electron gas (2DEG) channel to the SiNx layer. Depletion of the 2DEG at positive bias in the negative sweeping direction indicates that the charges injected have a long decay time, which was also observed in the recovery process of the capacitance after injection. The tunneling induced electron transfer effect in SiNx/Al0.22Ga0.78N/GaN based MIS structure opens up a way to design AlxGa1−xN/GaN based variable capacitors and memory devices.  相似文献   

7.
The electronic and structural properties of zigzag aluminum nitride (AlN), gallium nitride (GaN) nanoribbons and AlxGa1−xN nanoribbon heterojunctions are investigated using the first-principles calculations. Both AlN and GaN ribbons are found to be semiconductor with an indirect band gap, which decreases monotonically with the increased ribbon width, and approaching to the gaps of their infinite two dimensional graphitic-like monolayer structures, respectively. Furthermore, the band gap of AlxGa1−xN nanoribbon heterojunctions is closely related to Al (and/or Ga) concentrations. The AlxGa1−xN nanoribbon of width n=8 shows a continuously band gap varying from about 2.2 eV-3.1 eV as x increases from 0 to 1. The large ranged tunable band gaps in such a quasi one dimension structure may open up new opportunities for these AlN/GaN based materials in future optoelectronic devices.  相似文献   

8.
In this work, the structure of InxGa1−xN/GaN quantum dots solar cell is investigated by solving the Schrödinger equation in light of the Kronig-Penney model. Compared to p-n homojunction and heterojunction solar cells, the InxGa1−xN/GaN quantum dots intermediate band solar cell manifests much larger power conversion efficiency. Furthermore, the power conversion efficiency of quantum dot intermediate band solar cell strongly depends on the size, interdot distance and gallium content of the quantum dot arrays. Particularly, power conversion efficiency is preferable with the location of intermediate band in the middle of the potential well.  相似文献   

9.
Electronic parameters of a two-dimensional electron gas (2DEG) in modulation-doped highly strained InxGa1−xAs/InyAl1−yAs coupled double quantum wells were investigated by performing Shubnikov-de Haas (S-dH), Van der Pauw Hall-effect, and cyclotron resonance measurements. The S-dH measurements and the fast Fourier transformation results for the S-dH at 1.5 K indicated the electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and satisfied qualitatively the nonparabolicity effects in the quantum wells. The electronic subband structures were calculated by using a self-consistent method.  相似文献   

10.
Semiconductor optoelectronic devices based on GaN and on InGaN or AlGaN alloys and superlattices can operate in a wide range of wavelengths, from far infrared to near ultraviolet region. The efficiency of these devices could be enhanced by shrinking the size and increasing the density of the semiconductor components. Nanostructured materials are natural candidates to fulfill these requirements. Here we use the density functional theory to study the electronic and structural properties of (10,0) GaN, AlN, AlxGa1 − xN nanotubes and GaN/AlxGa1 − xN heterojunctions, 0<x<1. The AlxGa1 − xN nanotubes exhibit direct band gaps for the whole range of Al compositions, with band gaps varying from 3.45 to 4.85 eV, and a negative band gap bowing coefficient of −0.14 eV. The GaN/AlxGa1 − xN nanotube heterojunctions show a type-I band alignment, with the valence band offsets showing a non-linear dependence with the Al content in the nanotube alloy. The results show the possibility of engineering the band gaps and band offsets of these III-nitrides nanotubes by alloying on the cation sites.  相似文献   

11.
The Shubnikov-de Haas (S-dH) results at 1.5 K for AlxGa1−xN/AlN/GaN heterostructures and the fast Fourier transformation data for the S-dH data indicated the occupation by a two-dimensional electron gas (2DEG) of one subband in the GaN active layer. Photoluminescence (PL) spectra showed a broad PL emission about 30 meV below the GaN exciton emission peak at 3.474 eV that could be attributed to recombination between the 2DEG occupying in the AlN/GaN heterointerface and photoexcited holes. A possible subband structure was calculated by a self-consistent method taking into account the spontaneous and piezoelectric polarizations, and one subband was occupied by 2DEG below the Fermi level, which was in reasonable agreement with the S-dH results. These results can help improve understanding of magnetotransport, optical, and electronic subband properties in AlxGa1−xAs/AlN/GaN heterostructures.  相似文献   

12.
Electron–electron interaction effect of the two-dimensional electron gas (2DEG) in AlxGa1−xN/GaN heterostructures has been investigated by means of magnetotransport measurements at low temperatures. From the temperature dependence of the longitudinal conductivity of the heterostructures, a clear transition region has been observed. Based on the theoretical analysis, we conclude that this region corresponds to the transition from the diffusive regime to the ballistic regime of the 2DEG transport property. The interaction constant is determined to be −0.423, which is consistent with the theoretical prediction. However, the critical temperature for the transition, which is 8 K in AlxGa1−xN/GaN heterostructures, is much higher than the theoretical prediction.  相似文献   

13.
The effect of hydrogen on donors and interface defects in silicon modulation doped AlxGa1−xAs/InyGa1−yAs/GaAs heterostructures has been investigated by photoluminescence (PL). Hydrogenation was carried out on two sets of samples, one set consists of high quality pseudomorphic heterostructures and another set having partially lattice relaxed structures prone to the defects. On exposure of high quality pseudomorphic structures to hydrogen plasma above 150 °C, a significant blue shift in the PL peak positions as well as bandwidth narrowing is observed. This indicates, the reduction in two-dimensional electron gas in the InyGa1−yAs quantum well due to hydrogen passivation of silicon donors in the AlxGa1−xAs supply layer. The reactivation of the donors is observed upon annealing the hydrogenated sample for 1 h at 250 °C under hydrogen ambient. Another interesting feature is a significant improvement in the PL of lattice-relaxed structures upon hydrogenation of the samples above 250 °C, which is attributed to the hydrogen passivation of interface defects due to the misfit dislocations.  相似文献   

14.
(Ga1−xMnx)N/GaN digital ferromagnetic heterostructures (DFHs) and (Ga1−xMnx)N/GaN grown on GaN buffer layers by using molecular beam epitaxy have been investigated. The photoluminescence (PL) spectra showed band-edge exciton transitions. They also showed peaks corresponding to the neutral donor-bound exciton and the exciton transitions between the conduction band and the Mn acceptor, indicative of the Mn atoms acting as substitution. The magnetization curves as functions of the magnetic field at 5 K indicated that the saturation magnetic moment in the (Ga1−xMnx)N/GaN DFHs decreased with increasing Mn mole fraction and that the saturation magnetic moment and the coercive field in the (Ga1−xMnx)N/GaN DFHs were much larger than those in (Ga1−xMnx)N thin films. These results indicate that the (Ga1−xMnx)N/GaN DFHs hold promise for potential applications in spintronic devices.  相似文献   

15.
Effects of the passivation of SiNx on the high temperature transport characteristics of the two-dimensional electron gas (2DEG) in unintentionally doped AlxGa1−xN/GaN heterostructures have been investigated by means of high temperature Hall measurements. The 2DEG density increases much after SiNx passivation, and the increment is proportional to the Si content in SiNx layer, indicating that the increment is mainly caused by ionized Si atoms at the SiN/AlxGa1−xN interface with dangling bonds or by Si atoms incorporated into the AlxGa1−xN layer during the SiNx growth, which is approved by strain analysis and X-ray photoemission spectroscopy (XPS). There is lower 2DEG mobility at room temperature in a passivated sample than in an unpassivated one. However, the 2DEG mobility becomes to be higher in a passivated sample than in an unpassivated one when the temperature is above 250 °C, which is suggested to be caused by different subband occupation ratios in the triangular quantum well at the heterointerface before and after passivation.  相似文献   

16.
The effect of Al mole fractions on the structural and electrical properties of AlxGa1−xN/GaN thin films grown by plasma-assisted molecular beam epitaxy (PA-MBE) on Si (1 1 1) substrates has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and current-voltage (I-V) measurements. X-ray results revealed that the AlGaN/GaN/AlN was epitaxially grown on Si substrate. By applying Vegard's law, the Al mole fractions of AlxGa1−xN samples were found to be 0.11, 0.24, 0.30 and 0.43, respectively. The structural and morphology results indicated that there is a relatively larger tensile strain for the sample with the smallest Al mole fraction; while a smaller compressive strain and larger grain size appear with Al mole fraction equal to 0.30. The strain gets relaxed with the highest Al mole fraction sample. Finally, the linear relationship between the barrier height and Al mole fraction was obtained.  相似文献   

17.
AlxInyGa1?x?yN quaternary alloys with different ratios of Al/In were grown by metal-organic chemical vapor deposition on GaN/Al2O3 substrates. The structural and emission properties of the as-grown samples were investigated, respectively, by high-resolution X-ray diffraction and photoluminescence (PL) measurements. The PL emission character is related to the two prominent quenching bands, which have been determined to be located at around 1.1 eV and 1.7 eV above the valence band, respectively, by the method of optical quenching of photoconductivity. PL emission is most intense when the Al/In ratio is 7.5 for the AlxInyGa1?x?yN layer. In addition, a stronger quenching phenomenon with Al/In ratio of 5.0 in AlxInyGa1?x?yN is observed in accordance with a reduction of the intensity of AlxInyGa1?x?yN-related emission peak.  相似文献   

18.
In order to design the optimal component structure of transmission-mode (t-mode) Ga1−xAlxN photocathode, the optical properties and quantum efficiency of Ga1−xAlxN photocathodes are simulated. Based on thin film principle, optical model of t-mode Ga1−xAlxN photocathodes is built. And the quantum efficiency formula is put forward. Results show that Ga1−xAlxN photocathodes can satisfy the need of detectors with “solar blind” property when the Al component is bigger than 0.375. There is an optimal thickness of Ga1−xAlxN layer to get highest quantum efficiency, and the optimal thickness is 0.3 μm. There is close relation between absorptivity and quantum efficiency, which is in good agreement with the “three-step” model. This work gives a reference for the experimental research on the Ga1−xAlxN photocathodes.  相似文献   

19.
Transmission electron microscopy (TEM) and photocurrent (PC) measurements were carried out to investigate the microstructural properties and excitonic transitions in InxGa1−xAs/In0.52Al0.48As multiple quantum wells (MQWs) for x = 0.54, 0.57 and 0.60. TEM images showed that high-quality 11-period InxGa1−xAs/In0.52Al0.48As MQWs had high-quality heterointerfaces. The results for the PC spectra at 300 K showed that the peaks corresponding to the excitonic transitions from the ground state electronic sub-band to the ground state heavy-hole band (E1-HH1) and the ground state electronic sub-band to the ground state light-hole band (E1-LH1) became closer to each other with decreasing In mole fraction and that E1-HH1 and E1-LH1 excitonic peaks shifted to longer wavelength with increasing applied electric field. The calculated values of the E1-HH1 interband transition energies were in qualitative agreement with those obtained form the PC measurements with and without applied electric field. These results can be helpful in understanding potential applications of InxGa1−xAs/InyAl1−yAs MQWs dependent on In mole fraction and applied electric field in long-wavelength optoelectronic devices.  相似文献   

20.
Based on effective-mass approximation, we present a three-dimensional study of the exciton in GaN/AlxGa1−xN vertically coupled quantum dots (QDs) by a variational approach. The strong built-in electric field due to the piezoelectricity and spontaneous polarization is considered. The relationship between exciton states and structural parameters of wurtzite GaN/AlxGa1−xN coupled QDs is studied in detail. Our numerical results show that the strong built-in electric field in the GaN/AlxGa1−xN strained coupled QDs leads to a marked reduction of the effective band gap of GaN QDs. The exciton binding energy, the QD transition energy and the electron-hole recombination rate are reduced if barrier thickness LAlGaN is increased. The sizes of QDs have a significant influence on the exciton state and interband optical transitions in coupled QDs.  相似文献   

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