Observation of differences in the quenching of the Photocurrent in GaAs containing EL2 and EL0

The quenching of the photocurrent and photo-Hall effect of several undoped semi-insulating gallium arsenide samples has been measured and compared with the deep-level photoluminescence spectra from neighboring samples. Samples that show either EL2 (0.68 eV) or ELO (0.63 eV) photoluminescence have distinctly different photocurrent quenching behaviors. EL2 samples show a photocurrent decrease of several orders of magnitude, and a change fromn-type to p-type conduction during quenching at 80 K with 1.1 eV light. ELO samples show a reduction in photocurrent of less than an order of magnitude with no change in the carrier type at this temperature. Photo-Hall effect experiments at 80 K indicate that the conduction isn-type for the ELO samples, but changes fromn- to p-type during the quench for the EL2 samples. The temperature dependence of the quenching has also been studied. EL2 samples show little variation in the range 10-80 K, while ELO samples show significant quenching similar to EL2 after the temperature is reduced below 70 K. These results indicate that defects other than EL2 can significantly affect photocurrent quenching experiments.     

掺In GaAs晶体中的EL2缺陷及其热处理

比较了掺Ｉｎ和非掺杂ＬＥＣ－ＧａＡｓ晶体中的ＥＬ２缺陷，分析了掺Ｉｎ量的不同与热处理过程的不同对ＬＥＣ－ＧａＡｓ晶体中ＥＬ２缺陷的影响。     

非掺杂半绝缘LECGaAs中电参数与碳浓度及EL2浓度的关系

利用范德堡方法和光吸收方法研究了非掺杂半绝缘（ＳＩ）ＬＥＣＧａＡｓ 中电参数与碳（Ｃ）浓度及ＥＬ２ 浓度的关系。通过比较实验结果和理论计算结果发现，这种半绝缘晶体中除Ｃ外还存在其它受主在电补偿中起重要作用     

未掺杂半绝缘GaAs中受主及电中性EL2分布的研究

测量了未掺杂半绝缘（ＳＩ）ＬＥＣＧａＡｓ中总的、电中性的ＥＬ２及净受主浓度分布和碳分布。结果表明，总ＥＬ２浓度径向分布呈Ｗ形而不是均匀的，净受主浓度径向分布呈∧形或∩形而不是Ｍ形。电中性ＥＬ２的Ｗ形径向分布由总ＥＬ２浓度的Ｗ形径向分布决定，而不是由于净受主的不均匀分布。有些样品中净受主浓度远大于碳浓度．意味着这些样品中除碳外还存在高浓度的其它受主。     

A comparison between atomic concentration profiles and defect density profiles in GaAs annealed after implantation with beryllium

Semi-insulating chromium-doped GaAs was implanted with 100 keV Be ions to fluences of 5 × 10¹³ and 1 × 10¹⁵ ions/cm². Specimens were annealed at 800°C for thirty minutes. Beryllium atomic concentration profiles, as determined by secondary ion mass spectrometry (SIMS), were compared to the defect density profiles obtained from transmission electron stereomicroscopy techniques for the annealed samples. A major redistribution of Be was observed compared to the as-implanted distribution after annealing at the higher fluence, whereas only a slight redistribution of Be occurred for the lower fluence. A major difference in the defect density profiles was observed with the fluences used for this study in the region where the annealed specimens were compared. The distribution of defects throughout the implanted-annealed layer was examined in GaAs annealed after implantation with the higher fluence using sectioned specimens. The relationships between the atomic Be concentration profile, the defect density profile, and the distribution of some specific defects were compared in these sectioned layers. The distribution and size of defects appear to be directly influenced by the Be concentration and its associated implantation induced damage.     

EL2能级对GaAs MESFET夹断电压的影响

在建立的理论模型基础之上,定量地分析了ＥＬ２能级对ＧａＡｓ ＭＥＳＦＥＴ夹断电压的影响,指出位于本征费米能级以下的ＥＬ２能级是影响ＧａＡｓ ＭＥＳＦＥＴ夹断电压大小的主要因素,ＥＬ２能级对ＧａＡｓ ＭＥＳＦＥＴ夹断电压的影响程度与ＥＬ２能给的缺陷密度呈线性关系。     

EL2能级和光电离截面的计算

我们采用EHT法计算了EL2缺陷模型的电子能级及其波函数,集团包含41个原子,用群论方法约化久期行列式。同时计算了该缺陷能级的光电离截面,计算结果与实验结果相符。     

Inhomogeneity of the deep center el2 in GaAs observed by direct infra-red imaging

The distribution of the dominant deep trap EL2 in 7.5cm diameter crystals of semi-insulating GaAs is studied by whole slice infrared imaging. Very significant fluctuations in the neutral EL2 concentration ([EL2]ℴ) are observed, corresponding at most to variations in [EL2]ℴ of up to 80%. The different sorts of fine structure, namely cell structure and bands of high infrared absorption ("sheets" and “streamers”) lying in (110) planes running down the <001> growth directions, are described.     

DETERMINATION OF TOTAL EL2 AND NET ACCEPTOR CONCENTRATION IN UNDOPED SI GaAs BY MULTI-WAVELENGTH INFRARED ABSORPTION METHOD

Total EL2 concentration distribution and net acceptor concentration distribution in uncloped semi-insulating(SI) LEC GaAs have been measured by multi-wavelength infrared absorption method. The experimental results indicate that total EL2 concentration radial distribution is W-shaped and net acceptor concentration radial distribution is sample-dependent, it can present a n shape, a A shape, or a W shape corresponding to different samples.     

Excitation photocapacitance study of EL2 in n-GaAs and its relation to non-stoichiometry

The excitation photocapacitance measurements are performed on n-GaAs to obtain charge transition characteristics of EL2 defects in a full spectral region. It is shown that the threshold photon energy for EL2⁺⁺ to EL2⁺ transition is changed as a function of the primary excitation photon energy. It is also shown that the Frank–Condon shifts (d_FC) changed. It is considered that the lattice relaxation around the EL2 defect is affected by the deviation from the stoichiometric composition.     

Accurate measurement of capture cross sections in deep level transient spectroscopy: Application to EL2 in GaAs

A rigorous formulation of capacitance changes during trap filling processes is presented and used to accurately determine the electron capture cross section of EL2 in GaAs at a particular temperature, 377K, in this case. The value, σ_n (377K) = 2.7 × 10⁻¹⁶ cm², is compared with that predicted from the emission dependence.     

A study of the transition from high to low resistivity in As-grown GaAs MBE material

This work discusses the transition from high resistivity as-grown GaAs layers to thermally metastable low resistivity as-grown layers by molecular beam epitaxy. This transition occurs at about 430°C and coincides with a reflective high energy electron diffraction reconstruction change from a 2 × 1 to 2 × 4 pattern for an As₄/Ga beam equivalent pressure ratio of 20. For growth temperatures in the range 350 to 430°C, room temperature Hall-effect measurements have shown resistivities of <10₇ ohm-cm and photoluminescence has shown new peaks at 0.747 eV and a band from 0.708 to 0.716 eV at 4.2K, in unannealed material.     

热处理改善未掺杂LEC GaAs中EL2分布均匀性机理的研究

根据ＥＬ２分布的热处理行为和Ａｓ沉淀分布特征的实验结果，讨论了Ａｓ沉淀对ＥＬ２分布的影响和热处理改善ＥＬ２分布均匀性的机理。     

热处理和淬火影响GaAs中EL2浓度机理的研究

对非掺杂(ND)半绝缘(SI)液封直拉(LEC)GaAs单晶在500～1170℃温度范围进行了单步和多步的热处理和淬火,研究了热处理及淬火对GaAs中EL2浓度的影响,讨论了热处理及淬火影响EL2浓度的机理.     

半绝缘砷化镓EPR谱的异常退火特性

中子辐照的水平生长出绝缘GaAs(样品A)、原生的和塑性形变的直法拉制半绝缘GaAs(样品C和D),都给出一组四线谱,但在不同的样品中呈现不同的退火特性:样品A经125℃三小时退火后,EPR谱有部分光猝灭效应,加长退火时间,光猝灭效应消失,表现出异常的退火特性;而样品C和D,则无光猝灭效应.     

Extraction of the defect density of states in microcrystalline silicon from experimental results and simulation studies

The constant photocurrent method in the ac-mode (ac-CPM) is used to determine the defect density of states (DOS) in hydrogenated microcrystalline silicon (μc-Si:H) prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD). The absorption coefficient spectrum (ac-α (hν)), is measured under ac-CPM conditions at 60 Hz. The measured ac-α (hν) is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band-tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. Independently, computer simulations of the ac-CPM are developed using a DOS model that is consistent with the measured ac-α (hν) in the present work and a previously measured transient photocurrent (TPC) for the same material. The DOS distribution model suggested by the measurements in the lower and in the upper part of the energy-gap, as well as by the numerical modelling in the middle part of the energy-gap, coincide reasonably well with the real DOS distribution in hydrogenated microcrystalline silicon because the computed ac-α (hν) is found to agree satisfactorily with the measured ac-α (hν).     

Study of defect levels in CdTe using thermoelectric effect spectroscopy

We have studied the defect levels in as grown and post growth processed cadmium telluride (CdTe) using thermoelectric effect spectroscopy (TEES) and thermally stimulated current (TSC) techniques. We have extracted the thermal energy (E_th) and trapping cross section (σ_th) for the defect levels using the initial rise and variable heating rate methods. We have identified 10 different defect levels in the crystals. Thermal ionization energy values obtained experimentally were compared to theoretical values of the transition-energy levels of intrinsic and extrinsic defects and defect complexes in CdTe determined by first-principles band-structure calculations. On the basis of this comparison, we have associated the observed ionization levels with various native defects and impurity complexes.     

Identification of the acceptor level V3+/2+ in GaAs and a new experimental observation of V2 in “low spin” ground state in GaAs

The results of optical absorption and deel level transient spectroscopy on various V-doped GaAs materials (n type Bridgman, n and p type liquid encapsulated Czochralski,n andp type liquid phase epitaxy) are reported. It is definitively shown that the single acceptor state of isolated vanadium is located atE _c -0.14 eV and that no mid gap-level related to isolated vanadium which could explain same reported semi-insulating properties of V-doped GaAs has been detected. From the analysis of the absolute photoionization cross section gs/sk _n ^o of the above level it is shown that V²⁺ is in a low spin state in accordance with recent theoretical predictions.     

氮气或氧气气氛退火的氧化铪材料电荷泄漏情况研究

本文中, 使用开尔文探针显微镜,研究了不同退火气氛(氧气或氮气)情况下氧化铪材料的电子和空穴的电荷保持特性。与氮气退火器件相比,氧气退火可以使保持性能变好。横向扩散和纵向泄露在电荷泄露机制中都起了重要的作用。 并且,保持性能的改善与陷阱能级深度有关。氮气和氧气退火情况下,氧化铪存储结构的的电子分别为0.44 eV, 0.49 eV,空穴能级分别为0.34 eV, 0.36 eV。 最后得到,不同退火气氛存储器件的电学性能也与KFM结果一致。对于氧化铪作为存储层的存储器件而言,对存储特性的定性和定量分析,陷阱能级,还有泄漏机制研究是十分有意义的。     

GaAs PHEMT材料中2DEG浓度的控制与测试研究

设计并使用分子束外延(MBE)方法制备了不同帽层厚度、不同掺杂浓度的双平面掺杂GaAs PHEMT外延材料,采用不同工艺手段控制InGaAs沟道异质结界面的平滑程度。采用非接触霍尔方法对样品二维电子气(2DEG)浓度及迁移率进行测试,并用范得堡法对实验结果加以验证。结果表明,平整异质结界面生长技术能有效控制高迁移率2DEG浓度分布;与范德堡法相比,非接触霍尔方法无破坏性、测试结果可靠,该结果可以用来分析多层结构的PHEMT外延材料中InGaAs沟道界面的生长情况。