掺杂GaAs/Al0.3Ga0.7As超晶格的光致发光特性分析

在室温下,通过光致发光实验研究了用MBE生长的GaAs/Al0.3Ga0.7As超晶格材料的光致发光特性,对测得的发光峰进行了指认.理论计算和实验结果符合很好.     

High uniformity of Al0.3Ga0.7As/ln0.15Ga0.85As doped-channel structures grown by molecular beam epitaxy on 3″ GaAs substrates

Al_0.3Ga_0.7As/ln_0.15Ga_0.85As doped-channel structures were grown by molecular beam epitaxy on 3″ GaAs substrates. The uniformities of electrical and optical properties across a 3″ wafer were evaluated. A maximum 10% variation of sheet charge density and Hall mobility was achieved for this doped-channel structure. A1 μm long gate field-effect transistor (FET) built on this layer demonstrated a peak transconductance of 350 mS/mm with a current density of 470 mA/mm. Compared to the high electron mobility transistors, this doped-channel FET provides a higher current density and higher breakdown voltage, which is very suitable for high-power microwave device applications.     

DX centers in Sn-doped Ga0.7Al0.3As

We have measured and analyzed the extended fine structure on the Sn K-shell x-ray absorption spectra of GaAs and Ga_0.7Al_0.3As doped with ∼5 x 10¹⁸ cm⁻³ Sn. Our results and their implications for the atomic structure of DX centers are discussed.     

Characteristics of Si3N4/GaAs metal-lnsulator-semiconductor interfaces with coherent Si/Al0.3Ga0.7As interlayers

Si₃N₄/GaAs metal-insulator-semiconductor (MIS) interfaces with Si(10Å)/ Al_0.3Ga_0.7As (20Å) interface control layers have been characterized using capacitance-voltage (C-V) and conductance methods. The structure was in situ grown by a combination of molecular beam epitaxy and chemical vapor deposition. A density of interface states in the 1.1 × 10¹¹ eV^-1 cm^-2 range near the GaAs midgap as determined by the conductance loss has been attained with an ex situ solid phase annealing of 600°C in N₂ ambient. A dip quasi-static C-V demonstrating the inversion of the minority-carrier verifies the decent interface quality of GaAs MIS interface. The hysteresis and frequency dispersion of the MIS capacitors were lower than 100 mV, some of them as low as 50 mV under a field swing of about ±2 MV/cm. The increase of the conductance loss at higher frequencies was observed when employing the surface potential toward conduction band edge, suggesting the dominance of faster traps. Self-aligned gate depletion mode GaAs metal-insulator-semiconductor field-effect transistors with Si/Al_0.3Ga_0.7As interlayers having 3 μm gate lengths exhibited a transconductance of about 114 mS/mm. The present article reports the first application of pseudomorphic Si/ Al_0.3Ga_0.7As interlayers to ideal GaAs MIS devices and demonstrates a favorable interface stability.     

GaAs/Al0.3Ga0.7As 量子阱红外探测器光谱特性研究

采用金属有机物化学气相沉积法(MOCVD)生长GaAs/Al0.3Ga0.7As量子阱材料,制备300 m300 m台面,内电极压焊点面积为20 m20 m,外电极压焊点面积为80 m80 m单元量子阱器件两种。利用傅里叶光谱仪对1#,2#样品进行77K液氮温度光谱响应测试。实验结果显示1#,2#样品峰值响应波长分别为8.43 m,8.32 m,与根据薛定谔方程得到器件理论峰值波长8.5 m间误差分别为1.0%,2.1%。实验结果说明MOCVD技术可以满足QWIP生长制备工艺要求,且器件电极压焊点位置与面积大小对器件峰值波长影响不大,而对峰值电流有一定影响。     

Femtosecond optical response of low temperature grown In0.53Ga0.47As

A femtosecond, tunable color center laser was used to conduct degenerate pump-probe transmission spectroscopy of thin film low temperature grown molecular beam epitaxy In_0.53Ga_0.47As samples. Low temperature molecular beam epitaxy In_0.53Ga_0.47As exhibits a growth-temperature dependent femtosecond optical response when probed near the conduction band edge. Below T_g=250°C, the optical response time of the material is subpicosecond in duration, and we observed induced absorption, which we suggest is due to the formation of a quasi-“three-level system”.     

Photoluminescence studies of In0.7Al0.3As/In0.75Ga0.25As/In0.7Al0.3As metamorphic heterostructures on GaAs substrates

The influence of the design of the metamorphic buffer of In_0.7Al_0.3As/In_0.75Ga_0.25As metamorphic nanoheterostructures for high-electron-mobility transistors (HEMTs) on their electrical parameters and photoluminescence properties is studied experimentally. The heterostructures are grown by molecular-beam epitaxy on GaAs (100) substrates with linear or step-graded In _x Al_{1 ? x} As metamorphic buffers. For the samples with a linear metamorphic buffer, strain-compensated superlattices or inverse steps are incorporated into the buffer. At photon energies ?ω in the range 0.6–0.8 eV, the photoluminescence spectra of all of the samples are identical and correspond to transitions from the first and second electron subbands to the heavy-hole band in the In_0.75Ga_0.25As/In_0.7Al_0.3As quantum well. It is found that the full width at half-maximum of the corresponding peak is proportional to the two-dimensional electron concentration and the luminescence intensity increases with increasing Hall mobility in the heterostructures. At photon energies ?ω in the range 0.8–1.3 eV corresponding to the recombination of charge carriers in the InAlAs barrier region, some features are observed in the photoluminescence spectra. These features are due to the difference between the indium profiles in the smoothing and lower barrier layers of the samples. In turn, the difference arises from the different designs of the metamorphic buffer.     

Electrical properties of molecular beam epitaxial GaAs grown at 300–450°C

We use the Hall effect and a new charge-transfer technique to study molecular beam epitaxial GaAs grown at the low substrate temperatures of 300–450°C. Layers grown from 350–450°C are semi-insulating (resistivity greater than 10⁷ Ω-cm), as grown, because of an As_Ga-related donor (not EL2) at E_C-0.65 eV. The donor concentrations are about 2×10¹⁸ cm⁻³ and 2×10¹⁷ cm⁻³ at growth temperatures of 300 and 400°C, respectively, and acceptor concentrations are about an order of magnitude lower. Relatively high mobilities (∼5000 cm²/V s) along with the high resistivities make this material potentially useful for certain device applications.     

Optimization of the In0.3Ga0.7As-Layer Thickness in a Triple-Junction In0.3Ga0.7As/GaAs/In0.5Ga0.5P Solar Cell

Semiconductors - The optimum absorbing-layer thickness in the bottom In0.3Ga0.7As subcell of a triple-junction In0.3Ga0.7As/GaAs/In0.5Ga0.5P solar cell is sought for using the Sentaurus TCAD...     

Effects of heat treatment on the 0.8 eV photoluminescence emission in GaAs grown by molecular beam epitaxy at low temperatures

We report 0.8 eV photoluminescence (PL) emission of GaAs grown at low temperatures between 325 and 400°C by molecular beam epitaxy. Effects of heat treatments of the 0.8 eV emission are compared with those of the 1.467 eV sharp bound exciton lines. This allows us to attribute the 0.8 eV emisson to the As-V_Ga center. We discuss the assigning of the As_i-V_Ga center to the well-known EL6. The PL intensity variation of 0.68 eV EL2 and 0.8 eV As_i-V_Ga seen in substrate materials is explained in terms of dislocation−mediated As_i-V_Ga transformation to EL2 whereas the PL intensity variation of 0.8 eV As_i-V_Ga for molecular beam epitaxy layers can be attributed to the growth condition.     

Very high-transconductance short-channel GaAs MESFETs with Ga0.3Al0.7As buffer layer

MESFETs with 0.17?m gate length were manufactured with an n+GaAs active layer (3 × 1018cm-3) and an undoped Ga0.3Al0.7As buffer layer grown by molecular-beam epitaxy. The deives showed very high transconductance (700mS/mm) with good pinchoff characteristics. The experimental transconductance values were compared with calculated ones using a model that assumed total carrier confinement within the active layer by a barrier potential at the GaAs/GaAlAs interface. The results suggest that very high-transconductance short-gate-length MESFETs can be fabricated with a heavily doped GaAs active layer provided that the carrier density in the active layer is maintained at the doping level.     

120-nm gate-length In0.7Ga0.3As/In0.52Al0.48As InP-based HEMT

120 nm gate-length In_(0.7)Ga_(0.3)As/In_(0.52)Al_(0.48) As InP-based high electron mobility transitions(HEMTs) are fabricated by a new T-shaped gate electron beam lithograph(EBL) technology,which is achieved by the use of a PMMA/PMGI/ZEP520/PMGI four-layer photoresistor stack.These devices also demonstrate excellent DC and RF characteristics:the transconductance,maximum saturation drain-to-source current,threshold voltage,maximum current gain frequency,and maximum power-gain cutoff frequency of InGaAs/I...     

Al0.98Ga0.02As的湿法氧化规律

为实现精确控制VCSELs器件中氧化孔的大小，对Al0.98Ga0.02As的湿法氧化规律进行了分析研究．首先运用一维Deal-Grove模型分析了Al0.98Ga0.02As条形台面湿法氧化的一般规律，并在此基础上进一步分析推导，加以适当的简化，提出了适用于二维圆形台面的简单氧化模型，用此模型模拟得到的结果与实验数据十分吻合．同时，实验中观察到氧化孔径很小时氧化速率突增的现象．运用这些规律，将氧化长度的精度控制在0.5μm内，基本实现了氧化工艺的可控性及可重复性．     

Transient current spectroscopy and frequency dispersion studies of low temperature GaAs and Al0.3Ga0.7As metal-insulator-semiconductor diodes

Low temperature (LT)-grown GaAs and Al_0.3Ga_0.7As metal-insulator-n⁺-GaAs (MIN) diodes have been fabricated and their electrical properties analyzed. Studies were carried out to evaluate the interfacial quality of the LT layer and the underlying n⁺-GaAs layer using transient current spectroscopy (TCS) and capacitance-frequency (C-f) characterization. TCS studies on LT-GaAs revealed a high concentration of a continuum of states anda dominant electron trap with an activation energy of 0.52eV. In LT-Al_0.3Ga_0.7As, a shallow trap at 0.36eV and two deep level traps at 0.85eV and 1.12eV were observed. Frequency dispersion was observed to be less for LT-GaAs samples with an AlAs barrier layer than without an AlAs barrier layer. However, LT-Al_0.3Ga_0.7As MIN diodes displayed a smaller frequency dispersion than LT-GaAs MIN diodes. Upon further investigation into MISFET devices, it was found that LT-Al_0.3Ga_0.7As MISFET devices had better transconductance frequency dispersion characteristics than LT-GaAs MISFET devices did.     

Photoluminescence study of the In0.3Ga0.7As surface quantum dots coupling structure

Photoluminescence (PL) was investigated as functions of the excitation intensity and temperature for a coupling surface quantum dots (SQDs) structure which consists of one In0.3Ga0.7As SQDs layer being stacked on multi-layers of In0.3Ga0.7As buried quantum dots (BQDs). Accompanied by considering the localized excitons effect induced by interface fluctuation, carrier transition between BQDs and SQDs were analyzed carefully. The PL measurements confirm that there is a strong carrier transition from BQDs to SQDs and this transition leads to obvious different PL characteristics between BQDs and SQDs. These results are useful for future application of SQDs as surface sensitive sensors.     

Investigation of DX centers in modulation-doped field-effect transistor-type Al0.3Ga0.7As/GaAs heterostructures using a fourier-transform deep level transient spectroscopy system

Al_0.3Ga_0.7As:Si/GaAs modulation-doped field-effect transistor-type heterostructures were grown using two different growth temperatures (500 and 620°C) and three doping modes (δ-doping, pulse-doping, and uniform-doping). Deep level transient spectroscopy (DLTS) measurements were performed on these structures using a new Fourier-analysis method. Up to four DLTS peaks, related to the different possible configurations of the nearest Al and Ga neighbors around each DX site, were observed. Both the growth temperature and the doping-mode are found to affect the DLTS spectra, in particular the number of observed peaks and their width. These results are interpreted in terms of the different mobilities of the Si doping atoms on the surface during growth.     

Hot-hole lateral transport in a two-dimensional GaAs/Al0.3Ga0.7As structure

A narrow peak at the leading edge of the current pulse was found in samples of p-GaAs/Al_0.3Ga_0.7As structures subjected to a high electric field. An analysis of the shape and height of the peak as a function of the electric field, as well as the field redistribution along the sample, allows us to conclude that domain instability exists under these conditions. It is also shown that the energy of holes heated in moderate electric fields can significantly exceed the optical phonon energy.     

DX-center energy level dependence on silicon doping concentration in Al0.3Ga0.7As

The Hall free carrier concentration of silicon-doped Al_0.3Ga_0.7As alloys is studied as a function of both temperature and illumination. Different thermal activation energies were observed for the DX center as a function of silicon concentration. Excitation of the samples using an infra-red source also provided data for better insight into the DX center population. We correlated the incremental free electron photo persistent population with the activation energies obtained from the temperature dependence of the measured Hall concentration. We concluded that large free carrier concentrations can yield perturbations in the lattice potential that may alter the configuration coordinate energy barriers for capture and emission of electrons by and from the DX centers.     

Persistent photo-conductance and photoquenching of selectively doped Al0.3Ga0.7As GaAs/heterojunctions

The dependence on photon energy of the persistent photoconductivity (PPC) in selectively doped high mobility Al_0.3Ga_0.7As—GaAs heterostructures has been measured at temperatures below 80 K. A decrease in conductivity due to light exposure at one wavelength after exposure to light at another wavelength — photo-quenching — is also found. It is concluded that deep centers in GaAs and AlGaAs other than the DX center in AlGaAs are mainly responsible for PPC.     

Growth of Al0.3Ga0.7As by molecular beam epitaxy in the forbidden temperature range using As2

Using a thermal cracker and polycrystalline arsenic source material, dimeric arsenic was obtained and utilised to grow Al0.3Ga0.7As layers in the temperature range of 600?700°C with excellent surface morphologies. It has been previously found that, with tetrameric arsenic, excellent surface morphologies were possible only below 630°C and above 690°. Based on these observations, it is postulated that above 630°C tetrameric arsenic has a surface lifetime that is too short to provide enough coverage even when the beam flux is increased dramatically. At and above 700°C, tetrameric arsenic is cracked more effectively by the surface energy gained from the substrate leading to a good surface coverage and to good surface morphologies.