Electrical measurements of bandgap shrinkage in heavily dopedp-type GaAs

Electron currents injected intop ⁺ -GaAs were measured by analyzing the collector current versus base-emitter voltage characteristics ofn-p ⁺ -n GaAs homojunction transistors. This technique facilitates accurate determination of electron injection currents forp-type GaAs doped greater than 10²⁰ cm⁻³. Previous experiments used a diode-based, sequential etch technique to demonstrate that so-called bandgap shrinkage effects substantially increase the electron current injected into p⁺-GaAs. However, the diode-based technique was limited to dopant concentrations ≤10¹⁹ cm⁻³. Using the homojunction transistor-based technique described in this paper, we report a similar enhancement of the electron current injected intop-type GaAs doped as heavily as 8 × 10¹⁹ cm⁻³.     

Co-Implantation and autocompensation in close contact rapid thermal annealing of Si-implanted GaAs:Cr

Close contact rapid thermal annealing of semi-insulating GaAs:Cr implanted with Si, Si + Al, and Si + P has been studied using variable temperature Hall effect measurements and low temperature (4.2K) photoluminescence (PL) spectroscopy. Isochronal (10 sec) and isothermal (1000° C) anneals indicate that As is lost from the surface during close contact annealing at high anneal temperatures and long anneal times. Samples which were implanted with Si alone show maximum activation at an annealing temperature of 900° C, above which activation efficiency decreases. Low temperature Hall and PL measurements indicate that this reduced activation is due to increasing auto-compensation of Si donors by Si acceptors at higher anneal temperatures. However, co-implantation of column V elements can increase the activation of Si implants by reducing Si occupancy of As sites and increasing Si occupancy of Ga sites, and therebyoffset the effects of As loss from the surface. For samples implanted with Si + P, activation increases continuously up to a maximum at an anneal temperature of 1050° C, and both low temperature Hall and PL measurements indicate that autocompensation does not increase in this case as the anneal temperature increases. In contrast, samples implanted with Si + Al show very low activation and very high compensation at all anneal temperatures, as expected. The use of column V co-implants in conjunction with close contact RTA can produce excellent donor activation of Si implanted GaAs.     

Process-induced stress and microcrack nucleation in GaAs wafers

Breakage of GaAs wafers during device fabrication leads to reduced yield and decreased quality control. Historically, wafer breakage that is not attributable to human or equipment errors has been assumed to be due to poor quality wafers. We present evidence that the probability of breakage during sub-micron GaAs device fabrication is a function of dielectric film edge stress, and not necessarily dependent on the magnitude of a critical flaw in the as-received wafer. X-ray residual stress measurements, x-ray topographic imaging, and three-point bend fracture measurements are used to determine the nature and origin of wafer breakage during those fabrication steps which induce large mechanical or thermal stresses. Our data show that the processing sequences that most influence wafer breakage are SiN passivation deposition and rapid thermal annealing implant activation. These processes are primarily responsible for large residual stresses developed in the near-surface layers of the GaAs substrate. For microelectronic applications, the existence of high film edge stresses nucleates microcracks, which further reduces fracture strength. The combined effects of high residual stress and low fracture strength make SiN passivated wafers more fragile (as compared to SiON passivated wafers), and therefore more likely to break during device processing.     

GaAs红外发光二极管加速寿命试验研究

本文采用步进应力的试验方法设计了一个针对GaAs红外发光二极管的可靠性加速寿命的研究方案.这种方法主要是把步进应力和恒定应力两种方法相结合,用此来评估GaAs红外发光二极管的可靠度;然后总结除了GaAs红外发光二极管这种光电器件的寿命分布形式和失效模式.     

GaAs/InP的键合界面热应力分析

采用双层条状金属热应力模型,用MATLAB方法对退火过程中GaAs/InP晶片间的应力和双轴弹性形变能进行模拟和分析。结果表明:将InP剪薄至200μm,GaAs剪薄至175μm,剪应力取得了一个相对的小值,而剥离应力更是被完全消除,这时正应力也相对较小。而按照一定的比例适度剪薄两侧晶片的厚度,可以使得两侧的双轴形变能减小到原来的一半以下。通过减薄键合晶片的厚度可以得到较好的键合质量。另外,不管那一种应力都随退火温度的升高而快速增加,所以实验中一定保持低的退火温度,通常小于300°C为宜。     

Current transport in fluorine implanted GaAs

Effects of fluorine implantation in GaAs have been investigated by electrical characterization. Ion implantation at 100 keV energy was conducted with doses of 10¹¹ and 10¹²/cm². The effect of fluorine implantation on current-voltage (I-V) characteristics of Schottky diodes was significant. Carrier compensation was observed after implantation by the improved I-V characteristics. The lower dose implanted samples showed thermionic emission dominated characteristics in the measurement temperature range of 300 to 100K. The starting wafer and the low dose implanted samples after rapid thermal annealing (RTA) showed similar I-V properties with excess current in the lower temperature range dominated by recombination. The higher dose implanted samples showed increased excess current in the whole temperature range which may result from the severe damage-induced surface recombination. These samples after RTA treatment did not recover from implantation damage as in the low dose implantation case. However, very good I-V characteristics were seen in the higher dose implanted samples after RTA. The influence of the higher dose ion implantation was to produce more thermal stability. The results show the potential application of fluorine implantation in GaAs device fabrication.     

Valence band offsets in strained GaAs1−xPx/GaAs heterojunctions

Valence band offsets at [100]-oriented heterojunctions between tensile-strained GaASj_1−xP_x and unstrained GaAs are studied experimentally and theoretically. Light-hole (LH) and heavy-hole (HH) offsets are first extracted from the well-width dependence of valence subband splittings observed in luminescence spectra of tensile-strained GaAs_1−xP_x/GaAs quantum wells of various compositions (x = 0.06,0.09, and 0.19). This data is then combined with results from two other laboratories, yielding a set of 30 independent experimental offset values for junctions with compositions throughout the range 0.06≤x ≤0.32. The data are found to be highly consistent, with linear fits δE_LH = −140x (meV) and δE_HH= −401x (meV) describing the measured offsets to within less than 5 meV on average. Experimental results are then compared with theoretical predictions for the GaAs_1−x P_x/GaAs system obtained from a tight-binding model for strained heterojunctions. Predictions from the tight-binding calculations are found to lie within experimental scatter for the LH offsets, which define the valence band edge in these heterostructures, while magnitudes of the tight-binding HH offsets exceed measured values by ~20% on average.     

Layer intermixing and related long-term instability in heavily carbon-doped AlGaAs/GaAs superlattices

Superlattices (SLs) of Al_o.3Ga_o.7As/GaAs grown by metalorganic chemical vapor deposition and heavily doped with carbon using CClp₄ were annealed for 24 h at 825° C under a variety of ambient and surface encapsulation conditions. Photoluminescence atT = 1.7 K has been employed to determine approximate Al-Ga interdiffusion coefficients (D _Ai-Ga) for different annealing conditions. For all encapsulants studiedD _Al-Ga increases with increasing As₄ pressure in the annealing ampoule. This result disagrees with trends reported for Mg-doped crystals, and with predictions of the charged point-defect (Fermilevel) model. The Si₃N₄ cap provides the most effecitve surface sealing against ambientstimulated layer interdiffusion (D _Al-Ga ≈ 1.5-3.9 x 10^-19 cm²/sec). The most extensive layer intermixing has occurred for an uncapped SL annealed under As-rich ambient (D _Al-Ga ≈ 3.3 x 10^-18 cm²/sec). These values are up to ~40 times greater than those previously reported for nominally undoped AIGaAs/GaAs SLs, implying that theC _As doping slightly enhances layer intermixing, but significantly less than predicted by the Fermi-level effect. The discrepancies between the experimental data and the model are discussed. Pronounced changes in the optical properties of the annealed SLs with storage time at room temperature are also reported. These changes may indicate a degraded thermal stability of the annealed crystals due to high-temperature-induced lattice defects. A possibly related effect of the systematic failure to fabricate buried heterostructure quantum well lasers via impurity-induced layer disordering in similarly doped AIGaAs/GaAs crystals is discussed.     

GaAs被动调Q固体激光特性研究

使用紧凑的直线平-凹腔结构,利用半导体饱和吸收片GaAs实现了二极管(LD)端面抽运Nd:GdVO4高重复频率的被动调Q 1.06μm激光运转,在8 W的泵浦功率下获得平均输出功率达0.98 W的稳定激光输出,最小脉冲宽度为60 ns.最高重复频率达240 kHz.     

激光诱导化学气相沉积法制备纳米晶硅的制备参数和退火工艺的研究

用CO2红外激光诱志化学气相沉积的方法制备纳米Si,激光强度越大,则SiH4受热温度越高,纳米Si的成核率越高,纳米Si核的密度越大,每一个核生长所吸收的Si原子数目越少,从而所得的纳米Si粒小而均匀。当激光强度减小到一个低限阈值,则SiH4温度太低,不能裂解。SiH4的流速越快,则纳米Si成核后生长期越短,纳米Si粒也小而均匀。当SiH4流速快到一个高限阈值,则SiH4受热时间太短,升不到裂解所需的高温。以上2个产生纳米Si的阈值正相关。纳米Si制取后退火脱H,3440cm^-1光谱带红移并增强,2150cm^-1光谱带形状变化,1100cm^-1光谱带形状变化,1100cm^-1光谱带由低频处蓝移而来并展宽。这都表明含O键在纳米Si很大的表面上出现。为了减轻含O键出现,纳米Si应在Ar气氛中而不是在空气中,从低于300℃的温度开始退火。     

Automated and calibrated whole wafer etch pit density measurements in GaAs

A technique for automated measurement of whole-wafer etch pit density (EPD) for GaAs wafers is presented. The technique relies on an infrared transmission experiment similar to that used to measure EL2 concentration. A theoretical relationship between transmission and EPD is established, including effects due to pit size. The new automated and old visual-count methods are compared on a 3“, low-pressure, liquid-encapsulated Czochralski wafer; it is established that the automated method has much better repeatability. An [EL2] map of this same wafer is also presented.     

Reversible electrical properties of LEC GaAs

Undoped, low-pressure, liquid-encapsulated Czochralski GaAs can be reversibly changed from conducting (ρ ∼ 1Ω-cm) to semi-insulating (ρ ∼ 10⁷Ω-cm) by either slow or fast cooling, respectively, after a 5 hr, 950° C soak in an evacuated quartz ampoule. The semi-insulating wafers are very uniform and lead to tight threshold-voltage control in direct-implant MESFET’s. We have studied crystals in both states by temperature-dependent Hall effect, photoluminescence, IR absorption, mass spectroscopy, and DLTS. It is shown that donor and acceptor concentrations are typically more than an order of magnitude greater than the C and Si concentrations, which are both less than 3 × 10¹⁴ cm⁻³. The EL2 concentration remains relatively constant at about 1.0 × 10¹⁶ cm⁻³. Thus, the normal EL2-Si-C compensation model does not apply. The most likely explanation for the reversibility involves a delicate balance between native-defect donors and acceptors in equilibrium at 950° C, but with the donors dominating after a slow cool, and the acceptors after a fast cool. A consistent model includes a dominant donor at E_c 0.13eV, probably V_As – As_Ga, and a dominant acceptor at E_v + 0.07eV, probably V_Ga Ga_As. In this model, vacancy motion is very important during the slow cool. Such processes must be strongly considered in the growth of bulk, high-purity GaAs.     

Photoresponse study of normal incidence detection in p-type GaAs/AIGaAs multiple quantum wells

We studied p-type GaAs/AIGaAs multiple quantum well (MQW) materials as a possible alternative to the current n-type GaAs/AIGaAs MQWs for infrared detection. The advantage of p-type MQWs is that absorption of infrared radiation at normal incidence is not selection rule forbidden as it is for the n-type. We have verified that significant photoresponse occurs at normal incidence in p-type MQWs. We studied changes in the photoresponse spectrum as a function of well width and temperature. The MQW heterostructures were designed to use bound to continuum intersubband absorption in the GaAs valence band and to have a peak photoresponse near 8 μm. The photoresponse spectrum was compared to the first theoretical model of the bound to continuum absorption in p-type GaAs/ AlGaAs MQWs. The theoretical absorption curve was found to be in good qualitative agreement with the experimental results.     

吸收因子对GaAs光导开关输出电压幅值的影响

研究了吸收因子与GaAs光导开关输出电压幅值的关系.考虑了开关电场对吸收系数的影响,导出了输出电压与吸收因子之间的函数关系式.在不同波长、间隙宽度、触发光脉冲能量条件下进行理论仿真,并与没有考虑吸收因子的情况相比,研究结果表明吸收因子对光导开关的输出电压幅值有重要影响,吸收因子减小了光导开关的输出电压幅值,延长了输出电压达到饱和状态的时间,增大了开关饱和触发光脉冲能量.在实际应用中应该对光导开关的吸收特性加以考虑.     

Investigation of high quality GaAs:In layers grown by liquid phase epitaxy

Indium-doped GaAs layers are investigated by low-field Hall effect, photoluminescence, and double crystal x-ray diffraction in order to study the influence of the In concentration on the electrical, optical, and crystallographic properties. The layers were grown by liquid phase epitaxy from solution with In concentrations in the range 0–10 at.%. It was found that epitaxial growth from the melt with 7 at.% In content produces the highest quality epitaxial layers.     

GaAs对脉冲Nd:YAG激光器的调Q和锁模

本文分析半导体材料GaAs对1064nm激光的可饱和吸收特性,在闪光灯抽运的平凹腔和平凸腔Nd:YAG激光器中,插入GaAs样品作为调Q器件,实现了激光器的被动调Q运转,分别获得脉冲宽度32.7ns(平凹腔)和30.9ns(平凸腔)的激光脉冲。实验上研究了平凹腔腔长和输出镜透过率对调Q激光输出性能的影响。当平凹腔腔长增加到125cm时,观察到GaAs对1064nm激光的被动锁模。对上述实验结果给予了合理的理论解释。     

Strain effects in CdTe (111) epitaxial layers grown on GaAs (100) substrates by molecular beam epitaxy

Spectroscopic ellipsometry and photoreflectance measurements on CdTe/GaAs strained heterostructures grown by moleculclr beam epitaxy were carried out to investigate the effect of the strain and the dependence of the lattice parameter on the CdTe epitaxial layer thicknesses. Compressive strains exist in CdTe layers thinner than 2 μm. As the strain increases, the value of the critical-point energy shift increases linearly. These results indicate that the strains in the CdTe layers grown on GaAs substrates are strongly dependent on the CdTe layer thickness. Author to whom all correspondence should be addressed.     

Prevention of thermal surface damage in GaAs by encapsulated annealing in an arsine ambient

This paper shows that both capped and capless techniques commonly used in the high temperature annealing of GaAs can cause thermal surface damage characterized by a decrease in the net carrier concentration in a region within a few micrometers of the surface. This thermal surface damage can be prevented by a technique of encapsulated annealing in an arsine ambient. Presented at the 26th Annual Electronic Materials Conference, Santa Barbara, CA, June 21, 1984.     

Defect state assisted tunneling in intermediate temperature molecular beam epitaxy grown GaAs

Current transport in molecular beam epitaxy (MBE) GaAs grown at low and intermediate growth temperatures is strongly affected by defects. A model is developed here that shows that tunneling assisted by defect states can dominate, at some bias ranges, current transport in Schottky contacts to unannealed GaAs material grown at the intermediate temperature range of about 400°C. The deep defect states are modeled by quantum wells which trap electrons emitted from the cathode before re-emission to semiconductor. Comparison of theory with experimental data shows defect states of energies about 0.5 eVbelow conduction band to provide the best fit to data. This suggests that arsenic interstitials are likely to mediate this conduction. Comparison is also made between as-grown material and GaAs grown at the same temperature but annealed at 600°C. It is suggested that reduction of these defects by thermal annealing can explain lower current conduction at high biases in the annealed device as well as higher current conduction at low biases due to higher lifetime. Quenching of current by light in the as-grown material can also be explained based on occupancy of trap states. Identification of this mechanism can lead to its utilization in making ohmic contacts, or its elimination by growing tunneling barrier layers.