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.     

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。     

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.     

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。     

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.     

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。     

PECVD SiO2 薄膜内应力研究

研究了等离子体增强化学气相淀积(PWCVD)法生长SiO2薄膜的内应力.借助XP-2型台阶仪和椭偏仪测量计算了SiO2薄膜的内应力,通过改变薄膜淀积时的工艺条件,如淀积温度、气体流量、反应功率、腔体压力等,分析了这些参数对SiO2薄膜内应力的影响.同时讨论了内应力产生的原因以及随工艺条件变化的机理,对工艺条件的优化有一定参考价值.     

ZnO-TiO2系微波介质陶瓷的相结构及研究进展

对ZnO-TiO2体系相结构进行了分析,并从制备工艺、掺杂改性和低温烧结三个方面综述了ZnO-TiO2系微波介质陶瓷的研究进展,提出ZnO-TiO2系微波介质陶瓷的主要发展方向:①掺杂金属阳离子改性;②采用物理方法(包括半化学法)降低颗粒半径,在提高反应活性的基础上,掺杂适量助烧剂,实现陶瓷的低温烧结。     

Highly transparent conductive films of thermally evaporated In2O3

Highly transparent (over 90% transmission in the visible range) and highly conductive (resistivity ≈2 × 10^-4 ohm-cm) indium oxide (undoped) films have been produced by thermal evaporation from In₂O₃ + In source in a vacuum chamber con-taining low pressures of O₂, . Film properties are comparable or superior to the best tin-doped indium oxide films that have ever been reported, and excellent reproducibility has been achieved. Hall effect measurements have revealed that the observed low resistivity is primarily a result of the excellent electron mobility (? 70 cm²/V-sec), although the electron concentration is also rather high (≥4 × l0²⁰/cm³). X-ray diffraction measurements show distinctly polycrystal-line In₂O₃ structure with a lattice constant ranging from 10.07Å to 10.11Å. Electrolytic electroreflectance spectra exhibit at least four critical transitions, from which we have determined the direct and indirect optical band gaps (3.56eV and 2.69eV, respectively). Burstein shifts due to the population of electrons in the condition band are also observed. From an internal photoemission study, the work function of the In₂O₃ film has been determined to be 5.0eV. These and other results, along with a discussion of the processing details are reported.     

二氧化碳激光在皮肤美容上的应用及临床观察

本文通过对皮肤良性肿瘤、病毒性皮肤病、色素障碍性皮肤病患者３２０人供５０３例皮损数的ＣＯ２激光治疗，从美容的角度探讨了治疗效果及技术要点。３２０个患者通过ＣＯ２激光治疗皮损痊愈４８９例，显效１２，有效２例；无效无例数，８例出现萎缩性疤痕，１例出现增生性疤痕。从而说明了只有掌握适用症及操作的技术要点，ＣＯ２激光是一种良好的皮肤病美容治疗手段。     

CO2激光联合明竹欣治疗尖锐湿疣临床观察

为评价CO2激光联合明竹欣口服治疗尖锐湿疣的临床效果。我们在CO2激光切除疣体的基础上应用明竹欣口服治疗尖锐湿疣80例,结果显示激光切除疣体联合明竹欣治疗尖锐湿疣治愈率达89.60%、术后复发率为10.40%,且整个治疗过程中未发现明显毒副反应。认为激光手术气化疣体联合明竹取是临床治疗尖锐湿疣较为安全有效的方法。     

CO_2激光联合奥平栓治疗尖锐湿疣临床观察

为评价CO2 激光联合奥平栓治疗尖锐湿疣的疗效。我们在CO2 激光切除疣体的基础上应用奥平栓治疗尖锐湿疣 4 0例。结果显示 ,激光切除疣体联合奥平栓治疗尖锐湿疣治愈率达 91 5 0 %、术后复发率为 8 5 0 %,显著高于单纯激光手术组的68 2 0 %(治愈率 )、3 1 80 %(复发率 ) ,且整个治疗过程中未发现明显毒副反应。认为激光手术气化疣体联合奥平栓是临床治疗尖锐湿疣较为安全有效的方法。     

Anomalous anisotropy in the absorption coefficient of vacancy-ordered Ga2Se3

The structural and optical properties of Ga₂Se₃ on (100)GaP and (100)GaAs prepared by molecular beam epitaxy have been investigated. The electron diffraction studies revealed that the superstructure was formed in [011] direction by the spontaneous ordering of native gallium-vacancies in the defect zinc blende structure under a selenium-rich growth condition, and very large absorption anisotropy (Δα>10⁴cm¹) was observed in the vacancy-ordered Ga₂Se₃. Furthermore, polarization dependence of photoconductivity due to the absorption anisotropy was observed in the vacancy-ordered Ga₂Se₃ on (100)GaAs.