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1.
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   

2.
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   

3.
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   

4.
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   

5.
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   

6.
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   

7.
(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   

8.
Unintentionally doped high-Al-content Al0.45Ga0.55N/GaN high electron mobility transistor (HEMT) structures with and without AlN interfacial layer were grown by metal-organic chemical vapor deposition (MOCVD) on two-inch sapphire substrates. The effects of AlN interfacial layer on the electrical properties were investigated. At 300 K, high two-dimensional electron gas (2DEG) density of 1.66 × 1013 cm−2 and high electron mobility of 1346 cm2 V−1 s−1 were obtained for the high Al content HEMT structure with a 1 nm AlN interfacial layer, consistent with the low average sheet resistance of 287 Ω/sq. The comparison of HEMT wafers with and without AlN interfacial layer shows that high Al content AlGaN/AlN/GaN heterostructures are potential in improving the electrical properties of HEMT structures and the device performances.  相似文献   

9.
The effects of the In-mole fraction (x) of an InxGa1−xN back barrier layer and the thicknesses of different layers in pseudomorphic AlyGa1−yN/AlN/GaN/InxGa1−xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non-linear Schrödinger-Poisson equations. Strain relaxation limits were also calculated for the investigated AlyGa1−yN barrier layer and InxGa1−xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed.  相似文献   

10.
GaN layers and Al1−xInxN/AlN/GaN heterostructures have been studied by scanning probe microscopy methods. Threading dislocations (TDs), originating from the GaN (0 0 0 1) layer grown on sapphire, have been investigated. Using Current-Atomic Force Microscopy (C-AFM) TDs have been found to be highly conductive in both GaN and AlInN, while using semi-contact AFM (phase-imaging mode) indium segregation has been traced at TDs in AlInN/AlN/GaN heterostructures. It has been assessed that In segregation is responsible for high conductivity at dislocations in the examined heterostructures.  相似文献   

11.
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   

12.
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   

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.
AlxGa1-x N/GaN调制掺杂异质结构的子带性质研究   总被引:1,自引:0,他引:1       下载免费PDF全文
通过低温和强磁场下的磁输运测量研究了Al0.22Ga0.78N/GaN调制掺杂异质结构中2DEG的子带占据性质和子带输运性质.在该异质结构的磁阻振荡中观察到了双子带占据现象,并发现2DEG的总浓度随第二子带浓度的变化呈线性关系.得到了该异质结构中第二子带被2DEG占据的阈值电子浓度为7.3×1012cm-2.采用迁移率谱技术得到了不同样品的分别对应于第一和第二子带的输运迁移率.发现当样品产生应变弛豫时第一子带的电子迁移 关键词: AlGaN/GaN异质结 二维电子气 子带占据 输运迁移率  相似文献   

15.
Using the Empirical Pseudopotential Method (EPM) combined with an improved Virtual Crystal Approximation (VCA), where the effect of compositional disorder is included as an effective periodic potential, we have calculated the electronic band structure of GaN and AlN under hydrostatic pressure up to 200 kbar and 160 kbar, respectively. The behavior of electronic properties of their alloys AlxGa1−xN in the wurtzite structure have been predicted at zero pressure, for the entire range of alloy concentrations.  相似文献   

16.
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   

17.
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   

18.
The structural and optical properties of an InxGa1−xN/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090 °C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure.  相似文献   

19.
The two-dimensional (2D) electron energy relaxation in Al0.25Ga0.75N/AlN/GaN heterostructures was investigated experimentally by using two experimental techniques; Shubnikov-de Haas (SdH) effect and classical Hall Effect. The electron temperature (Te) of hot electrons was obtained from the lattice temperature (TL) and the applied electric field dependencies of the amplitude of SdH oscillations and Hall mobility. The experimental results for the electron temperature dependence of power loss are also compared with the current theoretical models for power loss in 2D semiconductors. The power loss that was determined from the SdH measurements indicates that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. In addition, the power loss from the electrons obtained from Hall mobility for electron temperatures in the range Te > 100 K is associated with optical phonon emission. The temperature dependent energy relaxation time in Al0.25Ga0.75N/AlN/GaN heterostructures that was determined from the power loss data indicates that hot electrons relax spontaneously with MHz to THz emission with increasing temperatures.  相似文献   

20.
We discuss problem of Rashba field in bulk GaN and in GaN/AlxGa1−xN two-dimensional electron gas, basing on results of X-band microwave resonance experiments. We point at large difference in spin-orbit coupling between bulk material and heterostructures. We observe coupled plasmon-cyclotron resonance from the two-dimensional electron gas, but no spin resonance, being consistent with large zero-field spin splitting due to the Rashba field reported in the literature. In contrast, small anisotropy of g-factor of GaN effective mass donors indicates rather weak Rashba spin-orbit coupling in bulk material, not exceed 400 G, αBIA<4×10−13 eVcm. Furthermore, we observe new kind of electron spin resonance in GaN, which we attribute to surface electron accumulation layer. We conclude that the sizable Rashba field in GaN/AlxGa1−xN heterostructures originates from properties of the interface.  相似文献   

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