GaAs MESFET栅取向效应中背栅的作用

根据压电效应模型,本文详细研究了压电电荷对GaAs MESFET沟道与衬底界面耗尽层的影响。认为正压电电荷比负压电电荷所引起的阀值电压漂移大,较好解释了(100)衬底上沿[011]和[011]取向的GaAs MESFET阈值电压非对称反向漂移的现象。     

Effect of substrate inhomogeneity on extrinsic photoconductivity of n-type GaAs thin-film structures under backgating

The extrinsic photoconductivity of n-type GaAs thin-film structures under backgating was studied. It is shown that the change of the spatial inhomogeneity of the substrate under illumination is responsible for a new mechanism of extrinsic photoconductivity under backgating. This mechanism occurs through an illumination-induced variation in the backgating threshold voltage and may result in a transition from positive to negative photoconductivity even if all deep levels in the substrate are electron traps. Experiments have shown that the onset of backgating and of negative differential conductivity coincide both in the dark and under illumination thus supporting the proposed mechanism.     

Velocity-field characteristics of electrons in doped GaAs

We report the first comprehensive measurements of the velocity-electric field charac-teristics of electrons in doped GaAs with carrier concentrations between 1 × 10¹⁵ and 1.5 × 10¹⁸ cm^s-3 at both 77 and 300 K. These measurements from 0 to 9000 V/cm make use of a 35 GHz technique in order to avoid charge domain formation which would render a DC measurement impossible in regions of negative differential resistance. We observe peak velocities at 300 K of between 0.9 × 10⁷ and 2.2 × 10⁷ cm/s in this doping range. Higher doping results in lower peak velocities which occur at higher electric fields. At 77 K, the trend is the same as at 300 K with peak velocities of between 1.1 × 10⁷ and 3.5 × 10⁷ cm/s. In addition, these measurements demonstrate anincrease in electron differential mobility in GaAs with increasing electric field. This effect occurs in moderately doped GaAs because the warm electrons which have been heated by the electric field scatter less efficiently with the ionized impurities than do the colder elec-trons. The increasing differential mobility occurs at electric fields well below the critical field for the onset of negative differential mobility and is more pronounced at 77 K than at 300 K. These results are significant both for the understanding of hot carrier trans-port in doped semiconductors as well as for understanding and modelling GaAs MESFETs.     

Comparison of OMVPE Grown GaAs/AlGaAs and GaAs/InGaP HEMT and PHEMT structures

Symmetric δ-doped InGaP and AlGaAs PHEMT structures have been grown by organometallic vapor phase epitaxy with properties that approach those of MBE grown AlGaAs structures. The 300 and 77K carrier concentrations for the InGaP PHEMT were 2.72 and 2.56 × 10¹² cm^{2 −2} and the mobilities were 5,920 and 22,000 cm^{2 2}/V.s. These excellent values suggest that problems associated with switching the anion at the channel heterojunction have been overcome. The corresponding values for the AlGaAs PHEMT were 2.51 and 2.19 × 10¹² cm^{2 −2} and 6,500 and 20,400 cm²/V.s. The uniformity in the indium concentration in the InGaAs layer as determined by photoluminescence, photoreflection, double crystal x-ray diffraction, and Rutherford backscattering was found to be good, but the percent In in the AlGaAs pseudo-morphic high electron mobility transistor (PHEMT) was less than that in the InGaP PHEMT even though the programmed values were the same. The uniformity in the doping distribution as determined by secondary ion mass spectroscopy and electrochemical capacitance-voltage measurements was found to be good, but it decreased with distance from the center of the susceptor. Also, most of the dopants in the δ-doped InGaP and AlGaAs layers were activated.     

Material characterization of an ion-implantation process for p-type (InGa)As/GaAs quantum-well structures

We have performed a detailed study of the formation of Be⁺-implanted contacts to modulation-doped, p-channel, (InGa)As/GaAs, single-strained quantum wells. Photoluminescence at 4 K from these structures is shown to be an excellent monitor of implant and annealing effects, as corroborated by Hall-effect measurements. Rapid thermal annealing produced higher electrical activation of the Be implants than did arsine-over-pressure annealing at comparable temperatures, similar to the trend in bulk GaAs. In contrast to conventional, alloyed-contact technologies, the rapid-annealed, implanted structures provided ohmic contact to the quantum well even at 4 K.     

Inclusion of impact ionization in the backgating of GaAs FETs

It is shown that the familiar threshold behavior of the backgate current of GaAs MESFETs has hysteresis. This is associated with an S-type negative differential conductivity (S-NDC) of the semi-insulating substrate. It is difficult to account for this hysteresis using conventional trap-fill-limited (TFL) theory, and it is attributed to the impact ionization of traps in the substrate. A simple model of this ionization, involving two trap levels, is used to incorporate its effect into an existing analytical model of GaAs FETs. The result is a qualitative interpretation of the backgating characteristics of GaAs MESFETs. The calculations show that a simple combination of two ohmic elements to represent parasitic resistances, and a nonohmic one to represent impact ionization in the substrate, can imitate the observed backgating behavior     

Effect of iso-electronic dopants on the dislocation density of GaAs

The addition of 1% In to LEC GaAs has been reported to reduce the dislocation density in this material; similar data exists for Sb doping. Several effects have been inferred to explain these phenomena, the most prevailing one stating that the solid stoichiometry is affected by an as yet unknown mechanism. Similar postulations have been made to explain the growth of semi-insulating GaAs. A thermodynamic model is described, based on earlier work, that shows a broadening of the existence region of GaAs when In or Sb are added to GaAs. Comparing the solidus phase diagrams of In- or Sb-doped GaAs to undoped GaAs shows that addition of either one of these two iso-electronic dopants has a similar effect on the solid stoichiometry as adding more As to the melt. However, the increased pressure problems in LEC growth of GaAs, normally associated with adding As, are circumvented if instead In or Sb are added to the melt. From our calculations it is also shown that the addition of the iso-electronic dopants Al or P to GaAs would not result in the same effect on the solid stoichiometry. Published experimental evidence supports this and shows that no dislocation reduction and semi-insulating GaAs is obtained with the use of these dopants. The model described in this paper explains the postulation that iso-electronic doping is of critical significance in controlling the solid stoichiometry and thereby obtaining zero dislocation density LEC GaAs and semi-insulating GaAs.     

Photoreflectance spectroscopy of low-dimensional GaAs/AlGaAs structures

Results of room-temperature photoreflectance measurements on three GaAs/Al_0.33Ga_0.67As multiquantum well (MQW) structures with three different widths of wells and on two GaAs/Al_0.33Ga_0.67As high-electron-mobility transistor (HEMT) structures are presented. Energy-gap-related transitions in GaAs and AlGaAs were observed. The Al content in AlGaAs was determined. MQW transition energies were determined using the first derivative of a Gaussian profile of the measured resonances. In order to identify the transitions in the MQS, the experimentally observed energies were compared with results of the envelope function calculation method for a rectangular quantum well. The Franz–Keldysh oscillation (FKO) model was also used to determine the built-in electric field in various parts of the investigated structures. The values of the electric fields allow us to hypothesise about the origin of these fields. © 1997 John Wiley & Sons, Ltd.     

Annealing behavior of InAs/GaAs quantum dot structures

We investigate the annealing behavior of InAs layers with different thicknesses in a GaAs matrix. The diffusion enhancement by strain, which is well established in strained quantum wells, occurs in InAs/GaAs quantum dots (QDs). A shift of the QD luminescence peak toward higher energies results from this enhanced diffusion. In the case of structures where a significant portion of the strain is relaxed by dislocations, the interdiffusion becomes negligible, and there is a propensity to generate additional dislocations. This results in a decrease of the QD luminescence intensity, and the QD peak energy is weakly affected.     

GaAs微结构中共振隧穿薄膜介观压阻效应研究

设计并利用控制孔技术加工了GaAs基微结构和基于该微结构的共振隧穿薄膜,并通过实验研究了微结构中共振隧穿薄膜的介观压阻效应,试验结果表明其介观压阻灵敏度比硅的最大压阻灵敏度高一个数量级.     

Comparison of InGaSb/InAs superlattice structures grown by MBE on GaSb, GaAs, and compliant GaAs substrates

This paper contains the characterization results for indium arsenide/indium gallium antimonide (InAs/InGaSb) superlattices (SL) that were grown by molecular beam epitaxy (MBE) on standard gallium arsenide (GaAs), standard GaSb, and compliant GaAs substrates. The atomic force microscopy (AFM) images, peak to valley (P-V) measurement, and surface roughness (RMS) measurements are reported for each sample. For the 5 μm×5 μm images, the P-V heights and RMS measurements were 37 ? and 17 ?, 12 ? and 2 ?, and 10 ? and 1.8 ? for the standard GaAs, standard GaSb, and compliant GaAs respectively. The high resolution x-ray diffraction (HRXRD) analysis found different 0^th order SL peak to GaSb peak spacings for the structures grown on the different substrates. These peak separations are consistent with different residual strain states within the SL structures. Depending on the constants used to determine the relative shift of the valance and conduction bands as a function of strain for the individual layers, the change in the InAs conduction band to InGaSb valance band spacing could range from +7 meV to −47 meV for a lattice constant of 6.1532 ?. The cutoff wavelength for the SL structure on the compliant GaAs, control GaSb, and control GaAs was 13.9 μm, 11 μm, and no significant response, respectively. This difference in cutoff wavelength corresponds to approximately a −23 meV change in the optical gap of the SL on the compliant GaAs substrate compared to the same SL on the control GaSb substrate.     

Preparation and properties of Zn delta-doped GaAs/AlGaAs heterojunction phototransistor

We have prepared, characterized and discussed the performance of AlGaAs/GaAs heterojunction bipolar phototransistor (HPT) including Zn delta-doped base. Due to the existence of δ-doped sheets located in the middle of undoped GaAs base the δ-doped HPT devices exhibit low dark current, nearly zero offset voltage, saturation voltage ∼0.4 V, and rise and fall times in ns range at wavelength of 850 nm up to 6 V of applied voltage. Due to avalanche multiplication behavior at the collector junction, an increased optical gain G>10 can be reached for applied voltages in the range of 6-12 V. For voltages higher than the device breakdown voltage (∼12 V) switching and negative differential resistance (NDR) effect is measurable in the inverted mode of operation.     

Influence of MBE growth temperature on GaAs/AlAs resonant tunneling structures

Double barrier GaAs/AlAs tunneling structures with typical 2.5:1 room temperature peak-to-valley current ratios are examined using Deep Level Transient Spectroscopy. Deep level trap concentrations are found to be much higher in samples grown at 550° C compared to those grown at 650° C. For devices grown at 550° C, an impedance switch-ing effect due to a high concentration of deep levels is observed. The peak-to-valley ratio of the tunneling devices is largely unaffected by the growth temperatures in this range, indicating that higher growth temperatures can be employed to grow resonant tunnel-ing diodes than previously suggested in the literature.     

The growth of buffered GaAs mesfet structures by LPE

Layers of LPE GaAs have been grown with background carrier levels in the low 10¹⁴ cm⁻³ range by systematic bakeouts of the Ga melts together with between-run loading in a dry N₂ environment. High resistivity layers in the range 10₃-10⁴Ω cm have been grown by making use of the compensation of free carriers by the out diffusion of Cr from the substrate. Intentional Cr-doping from the melt resulted in layers with poor surface morphologies. Buffered MESFET structures have been grown which show near ideal carrier concentration profiles and which do not exhibit interfacial space charge effects.     

一种指数掺杂的砷化镓平面肖特基变容二极管的设计与制作

利用标准微电子工艺研制出了一种可以应用于微波倍频电路中的肖特基势垒变容二极管,采用平面结构的制作工艺,克服了传统制作工艺的不易集成的缺点.并且在N型层的掺杂浓度呈指数规律,使变容管的变容比高于传统的均匀掺杂结构,有利于提高倍频电路的工作频率和输出功率.采用台面隔离工艺以形成分别用于制作肖特基接触和欧姆接触的两个台面.经...     

A THz-range planar NDR device utilizing ballistic electron acceleration in GaN

A planar and ultra-short gallium nitride (GaN) diode structure is investigated as a potential Terahertz (THz) range negative differential resistance (NDR) diode. An empirical velocity-field relation, exhibiting a peak electron velocity as high as 7 × 10⁷ cm/s, is employed to characterize the high-field transport in the simulations, accounting for ballistic electron acceleration and velocity reduction due to phonon build up. The resulting device operation is in accumulation-layer transit-time mode and large-signal circuit simulation results are reported along with discussions. Conversion efficiencies up to ∼3.4% at ∼1.5 THz are shown to be possible.     

GaAs-LED阵列器件隔离沟槽的制备研究

良好的电学和光学隔离能显著提高微LED阵列器件的亮度、分辨率等工作性能,高深宽比隔离沟槽的制备是决定电学隔离效果的关键。本文分析比较了各种制备工艺,选择湿法腐蚀工艺,使用了不同比例柠檬酸双氧水腐蚀液对GaAs进行了腐蚀,在二者配比为3：1的条件下,在GaAs衬底材料上制备了深宽比为2：1的隔离沟槽。腐蚀后芯片表面平整度、侧蚀等指标初步达到器件设计的要求。     

Hot phonons and instabilities in GaAs/GaAlAs structures

We report experimental observations concerning high field parallel transport in GaAs/GaAlAs quantum-well structures comparing degenerate and non-degenerate material. Hot electron photoluminescence measurements show hot-phonon reduction of the energy relaxation rates in degenerate material as compared with that in non-degenerate material in agreement with a simple model of transport involving hot phonon effects. The latter predicts a reduction in drift velocity at high fields compared with that in bulk material and this is observed in our specimens. Hot phonons are shown to inhibit instabilities. Non degenerate samples exhibit current instabilities much more readily than degenerate material. In the latter, the hot phonon reduction in drift velocity will tend to inhibit NDR via real space transfer or via intervalley transfer.     

High temperature MOVPE growth of GaAs/AlGaAs device structures with tertiarybutylarsine

The performance characteristics of epitaxial structures suitable for optoelectronic and electronic devices were investigated. These were fabricated by MOVPE using tertiary-butylarsine, a non-hydride arsenic source. Minority carrier diffusion lengths of 5μm at 3 × 10¹⁸/cm³ and 2μm at 2 × 10¹⁹/cm³ were achieved inp-type GaAs. Recombination velocities at the GaAs/AlGaAs interface are reduced to 1 × 10³ cm/sec by processing under appropriate conditions. Electron mobilities of 4000 cm²/V-sec inn-type (2 × 10¹⁷/cm³) layers resulted in transconductances of 120 mS/mm in 1.5μm gate depletion mode MESFETs. The above values are comparable to those obtained with arsine in this work and others reported in the literature.