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.     

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...     

Microwave performance of 0.4 mu m gate metamorphic In/sub 0.29/Al/sub 0.71/As/In/sub 0.3/Ga/sub 0.7/As HEMT on GaAs substrate

MBE grown metamorphic In/sub 0.29/Al/sub 0.71/As/In/sub 0.3/Ga/sub 0.7/As/GaAs high electron mobility transistors (HEMTs) have been successfully fabricated. A 0.4 mu m triangular gate device showed transconductance as high as 700 mS/mm at a current density of 230 mA/mm. The measured f/sub T/ was 45 GHz and f/sub max/ was 115 GHz. These high values are, to the authors knowledge, the first reported for submicrometre metamorphic InAlAs/InGaAs/GaAs HEMTs with an indium content of 30%.<>     

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.     

Hall and photoluminescence studies of effects of the thickness of an additional In0.3Ga0.7As layer in the center of In0.15Ga0.85As/Al0.25Ga0.75As/GaAs high electron mobility transistors

In order to reduce the noise and carrier–donor scattering and thereby increase the carrier mobility of the pseudomorphic AlGaAs/InGaAs high electron mobility transistors (pHEMTs), we have grown Al_0.25Ga_0.75As/In_0.15Ga_0.85As/In_0.3Ga_0.7As/GaAs pHEMTs with varied In_0.3Ga_0.7As thickness, and studied the effects of the In_0.3Ga_0.7As thickness on the electron mobility and sheet density by Hall measurements and photoluminescence measurements. We calculated the electron and hole subbands and obtained good agreement between calculated and measured PL energies. It was found that the additional In_0.3Ga_0.7As layer could be used to reduce the carrier–donor scattering, but due to the increased interface roughness as the In_0.3Ga_0.7As layer becomes thicker, the interface scattering reduced the electron mobility. An optimal thickness of the In_0.3Ga_0.7As was found to be 2 nm.     

Application of photoluminescence spectroscopy to studies of In0.38Al0.62As/In0.38Ga0.62As/GaAs metamorphic nanoheterostructures

The results of studies of the surface morphology, electrical parameters, and photoluminescence properties of In_0.38Al_0.62As/In_0.38Ga_0.62As/In_0.38Al_0.62As metamorphic nanoheterostructures on GaAs substrates are reported. Some micron-sized defects oriented along the [011] and \([0\bar 11]\) directions and corresponding to regions of outcropping of stacking faults are detected on the surface of some heterostructures. The Hall mobility and optical properties of the samples correlate with the surface defect density. In the photoluminescence spectra, four emission bands corresponding to the recombination of charge carriers in the InGaAs quantum well (1–1.2 eV), the InAlAs metamorphic buffer (1.8–1.9 eV), the GaAs/AlGaAs superlattice at the buffer-substrate interface, and the GaAs substrate are detected. On the basis of experimentally recorded spectra and self-consistent calculations of the band diagram of the structures, the compositions of the alloy constituents of the heterostructures are established and the technological variations in the compositions in the series of samples are determined.     

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...     

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。     

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.     

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.     

Al/sub 0.25/Ga/sub 0.75/As/In/sub 0.25/Ga/sub 0.75/As pseudomorphic MODFET with high DC and RF performance

AlGaAs/InGaAs MODFETs having 25% indium in the channel and L/sub G/=0.35 mu m have been fabricated. From DC device characterisation, a maximum saturation current of 670 mA/mm and an extrinsic transconductance of 500 mS/mm have been measured. A maximum unilateral gain cutoff frequency of f/sub c/=205 GHz and a maximum current gain cutoff frequency of f/sub T/=86 GHz have been achieved. Bias dependence of f/sub c/ and f/sub T/ has been measured. At 12 GHz a minimum noise figure of NF=0.8 dB and an associated gain of 11 dB have been measured.<>     

Hydrogen plasma passivation of bulk GaAs and Al0.3Ga0.7As/GaAs multiple-quantum-well structures on Si substrates

Hydrogen (H) plasma passivation effects on GaAs grown on Si substrates (GaAs on Si) are investigated in detail. H plasma exposure effectively passivates both the shallow and deep defects in GaAs on Si, which improves both the electrical and optical properties. It was found that the minority carrier lifetime is increased and the deep level concentration is decreased by the H plasma exposure. In addition, after H plasma exposure, room temperature photoluminescence (PL) for Al_0.3Ga_0.7As/GaAs multiple-quantum-well (MQW) on Si is enhanced with a decrease in the spectral width.     

Light sensitivity of Al0.25Ga0.75As/GaAs modulation-doped structures grown by molecular beam epitaxy: effect of substrate temperature

The sensitivity of carrier concentration and mobility of Al0.25Ga0.75As/GaAs modulation-doped structures to light exposure has been studied. The light sensitivity of both parameters was found to be strongly dependent on the growth temperature of the Al0.25Ga0.75As which was varied between 580°C and 695°C. A growth temperature of about 610°C was observed to produce the least light sensitivity, while a growth temperature of 660°C resulted in the most sensitivity to light. The corresponding minimum and maximum changes in carrier concentration, measured at 10 K, were 5% and 52% of the dark values, respectively, while changes in mobility were 2% and 40%, respectively. A persistent photoconductivity effect was also observed in the samples. The minimum in this effect was found to be a 1% change in 10 K carrier concentration at a growth temperature of 610°C.     

Very low-noise Al/sub 0.3/Ga/sub 0.7/As/Ga/sub 0.65/In/sub 0.35/As/GaAs single quantum-well pseudomorphic HEMTs

AlGaAs/GaInAs/GaAs pseudomorphic HEMTs with an InAs mole fraction as high as 35% in the channel has been successfully fabricated. The device exhibits a maximum extrinsic transconductance of 700 mS/mm. At 18 GHz, a minimum noise figure of 0.55 dB with 15.0 dB associated gain was measured. At 60 GHz, a minimum noise figure as low as 1.6 dB with 7.6 dB associated gain was also obtained. This is the best noise performance yet reported for GaAs-based HEMTs.<>     

Nanorelief of an oxidized cleaved surface of a grid of alternating Ga0.7Al0.3As and GaAs heterolayers

The morphology of an oxidized cleaved surface of a grid of alternating GaAs and Ga_0.7Al_0.3As layers was investigated by atomic-force microscopy. It was found that the surface of the native oxide film on a cleaved surface possesses a quasistationary nanorelief that reflects the composition of the layers of the heterostructure. The oxide regions above the GaAlAs layers are 0.5 nm higher than the regions above the GaAs layers. Etching off the oxide film shows that a nanorelief, which is inverted with respect to the relief of the oxide surface, also forms on the bared cleaved surface. The appearance of nanoreliefs on the surface and at the bottom boundary of the native oxide film is explained by the different oxidation depths of GaAs and Ga_0.7Al_0.3As and by an oxidation-induced increase in the volume. Fiz. Tekh. Poluprovodn. 33, 594–597 (May 1999)     

Al/sub 0.3/Ga/sub 0.7/As/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) doped-channel field-effect transistors (DCFET's)

The properties of both lattice-matched and strained doped-channel field-effect transistors (DCFET's) have been investigated in AlGaAs/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) heterostructures with various indium mole fractions. Through electrical characterization of grown layers in conjunction with the dc and microwave device characteristics, we observed that the introduction of a 150-/spl Aring/ thick strained In/sub 0.15/Ga/sub 0.85/As channel can enhance device performance, compared to the lattice-matched one. However, a degradation of device performance was observed for larger indium mole fractions, up to x=0.25, which is associated with strain relaxation in this highly strained channel. DCFET's also preserved a more reliable performance after biased-stress testings.<>     

InAs/GaAs quantum dot infrared photodetector (QDIP) with double Al/sub 0.3/Ga/sub 0.7/As blocking barriers

The ten stacked self-assembled InAs/GaAs quantum dot infrared photodetectors (QDIP) with different Al/sub 0.3/Ga/sub 0.7/As barrier widths and growth temperatures were prepared. Asymmetric current-voltage (I-V) characteristics and 2/spl sim/7.5 /spl mu/m detection window were observed. Peak responsivity of 84 mA/W at -0.4 V and peak specific detectivity of 2.5/spl times/10/sup 9/ cm-Hz/sup 1/2//W at zero bias were observed at 50 K. The characteristics of polarization insensitivity over the incident light and the high background photocurrent suggest that the self-assembled QDIP can be operated at higher temperature (/spl sim/250 K) under normal incidence condition in contrast to quantum well infrared photodetector (QWIP).     

不同缓冲层对GaAs基In_(0.3)Ga_(0.7)As材料特性的影响

采用组分跳变和低温大失配缓冲层技术在GaAs衬底上外延了In0.3Ga0.7As材料。测试结果表明,采用组分跳变缓冲层生长的In0.3Ga0.7As主要依靠逐层间产生失配位错来释放应力,并导致表面形成纵横交错的Cross-hatch形貌;而采用低温大失配缓冲层技术则主要通过在低温缓冲层中形成大量缺陷来充分释放应力,并在后续外延的In0.3Ga0.7As表面没有与失配位错相关的Cross-hatch形貌出现。此外,仅需50nm厚的低温大失配缓冲层即可促使In0.3Ga0.7As中的应力完全释放,这种超薄缓冲层技术在工业批产中显得更为经济。     

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.