Effect of ion implantation on quantum well infrared photodetectors

Ion implantation is a postgrowth processing technique which, when combined with annealing, can be used to tune the absorption wavelength of quantum well devices. We have implanted and annealed, three different quantum well infrared photodetector structures, and measured the absorption spectra of the samples by Fourier transform spectroscopy. The peak absorption wavelength shift of each structure has been calculated as a function of diffusion length by simulating the diffusion processes. We found different diffusion rates for the structures and attribute this to different numbers of as-grown defects. Our results indicate that agglomeration of single defects into defect clusters limits the ability of ion implantation to tune the wavelength of a structure with a higher number of as-grown defects. Thus, a structure with the lowest number of as-grown defects is most useful for fabricating a multi-color quantum well photodetector by ion implantation, because in this case ion implantation can enhance the diffusion rate considerably leading to large red- shift in peak absorption wavelength.     

Evidence of the Zn vacancy acting as the dominant acceptor in n-type ZnO

We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (E(el)=2 MeV, fluence 6 x 10(17) cm(-2)) ZnO samples. The Zn vacancies are identified at concentrations of [V(Zn)] approximately 2 x 10(15) cm(-3) in the as-grown material and [V(Zn)] approximately 2 x 10(16) cm(-3) in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.     

室温下(Ga,Mn)As中载流子的自旋弛豫特性

运用飞秒时间分辨抽运-探测克尔光谱技术,研究了室温下退火及未退火(Ga,Mn)As的载流子自旋弛豫的激发能量密度依赖性,发现电子自旋弛豫时间随激发能量密度增加而增大,而在同一激发能量密度下,退火样品比未退火样品具有更短的载流子复合时间、电子自旋弛豫时间和更大的克尔转角,显示DP机理是室温下(Ga,Mn)As的电子自旋弛豫的主导机理.退火(Ga,Mn)As的超快克尔增强效应显示其在超高速全光自旋开关方面的潜在应用价值,也为(Ga,Mn)As铁磁性起源的p-d交换机理提供了证据. 关键词： (Ga Mn)As稀磁半导体 时间分辨克尔光谱 电子自旋弛豫 DP机理     

Investigation of luminescence processes in YAG single crystals irradiated by 50 MeV electron beam

Absorption, emission and excitation spectra of 50 MeV electron beam irradiated and as-grown YAG single crystals were studied and compared in the 10–300 K temperature range using time-resolved luminescence spectroscopy under UV/VUV/XUV excitation by synchrotron radiation and cathodoluminescence. The emission spectra consist of intrinsic (excitonic) and defect related non-elementary bands in the VIS/UV range. It is shown that fast electrons create stable F and F⁺ color centers with characteristic emission and absorption bands in the visible/UV range. Induced absorption caused from these defects starts at 4.2 eV. Energy transfer from host to color centers is not an efficient process.     

Revised calculation of point defect equilibria and non-stoichiometry in gallium arsenide

From an analysis of relevant published literature, it is deduced that the dominant disorder in GaAs is Frenkel defect formation on the arsenic sub-lattice with the arsenic vacancy exhibiting donor-like behaviour at high temperatures. Standard methods of chemical thermodynamics are used to derive expressions for the concentrations of the neutral and charged point defects. Mass action constants are obtained from a combination of a priori estimates and fitting to experimental data. The phase extent of GaAs is mapped and the model shown to account adequately for the density, lattice parameter and internal friction variations in as-grown and heat treated material as well as for the high temperature Hall coefficient behaviour.     

Thermally induced native defect transform in annealed GaSb

Undoped p-type Ga Sb single crystals were annealed at 550–600?C for 100 h in ambient antimony. The annealed Ga Sb samples were investigated by Hall effect measurement, glow discharge mass spectroscopy(GDMS), infrared(IR)optical transmission and photoluminescence(PL) spectroscopy. Compared with the as-grown Ga Sb single crystal, the annealed Ga Sb samples have lower hole concentrations and weak native acceptor related PL peaks, indicating the reduction of the concentration of gallium antisite related native acceptor defects. Consequently, the below gap infrared transmission of the Ga Sb samples is enhanced after the thermal treatment. The mechanism about the reduction of the native defect concentration and its influence on the material property were discussed.     

The important features of VHg-related defects in arsenic-doped HgCdTe

The as-grown arsenic-doped HgCdTe typically exhibits compensated n-type conductivity. Based on first-principles calculations, we identify Hg vacancies (V_Hg) as a dominant defect species involved in the compensation. Arsenic donor (As_Hg) and V_Hg acceptor no doubt tend to combine into complex defects but little has been recognized about the features of the complex defects in precious studies. These features outlined in this work enable us to provide a consistent explanation for arsenic activation mechanism proposed by Zandian et al. [7] and Berding et al. [8].     

Z1/Z2 defects in 4H-SiC

First-principles calculations are carried out on models for the Z(1)/Z(2) defects in 4H-SiC which are found in as-grown and irradiated n-type material. We show that an interstitial-nitrogen-interstitial-carbon defect is exceptionally thermally stable, bistable, and has negative-U character with donor and acceptor levels close to those attributed to the defect.     

Charge-sensitive deep level transient spectroscopy of helium-ion-irradiated silicon, as-irradiated and after thermal annealing

Electrically active defects in the phosphor-doped single-crystal silicon, induced by helium-ion irradiation under thermal annealing, have been investigated. Isothermal charge-sensitive deep-level transient spectroscopy was employed to study the activation energy and capture cross-section of helium-induced defects in silicon samples. It was shown that the activation energy levels produced by helium-ion irradiation first increased with increasing annealing temperature, with the maximum value of the activation energy occurring at 873K, and reduced with further increase of the annealing temperature. The energy levels of defects in the samples annealed at 873 and 1073K are found to be located near the mid-forbidden energy gap level so that they can act as thermally stable carrier recombination centres.     

Relationship of annealing time and intrinsic defects of unintentionally doped 4H-SiC

With annealing temperature kept at 1573 K, the effects of annealing time on stability of the intrinsic defects in epitaxial unintentionally doped 4H-SiC prepared by low pressure chemical vapour deposition have been studied by electron spin resonance (ESR) and low temperature photoluminescence. This paper reports the results shown that annealing time has an important effect on the intrinsic defects in unintentionally doped 4H-SiC when annealing temperature kept at 1573 K. When the annealing time is less than 30 min, the intensity of ESR and photoluminescence is increasing with annealing time prolonged, and reaches the maximum when annealing time is 30 min. Then the intensity of ESR and photoluminescence is rapidly decreased with the longer annealing time, and much less than that of as-grown 4H-SiC when annealing time is 60 min, which should be related with the interaction among the intrinsic defects during the annealing process.     

Photothermal deflection spectroscopy study of defects in semi-insulating GaAs

Subgab absorption measurements carried out by photothermal deflection spectroscopy in semi-insulating GaAs are used to study the concentration of defects found in as-grown and in heat treated material. Measurements carried out in ion-implanted and furnace-annealed samples prove to be a useful tool for monitoring the successful recovery of the ion implantation damage.     

直拉硅单晶原生漩涡缺陷的研究

本文用化学腐蚀方法, 从含有漩涡缺陷的原生CZ硅单晶中分离出尺寸在1000--6000埃间的氧沉淀, 制成萃取复型样品,用T E M 对氧沉淀作微区电子衍射分析. 同时, 观察硅薄膜中漩涡缺陷的TEM 象, 确定了二者的对应关系. 结果表明, 构成漩涡缺陷的氧沉淀主要是呈方形片的热液石英(keatite, siliea k) 及少量呈六角片的。方英石(a-cristobalite ), 沉淀片周边沿<1 1 0> 方向, 惯习面前者的为{ 100} , 后者的为{ 1 1 1}. 样品的红外吸收光谱表明, 方片状热液石英沉淀可能与1 2 2 4 (1/cm ), 吸收峰相对应. 关键词：     

Electron irradiation-induced defects in lithium doped n-type silicon with different oxygen concentrations

Electron irradiation-induced defects and their annealing behaviour in lithium (Li) doped n-type silicon containing different oxygen concentrations have been studied with deep level transient spectroscopy (DLTS) in conjunction with the capacitance-voltage (C-V) method. Two Li-related defects E(0.17) and E(0.50) situated at, respectively, 0.17 and 0.50 eV below the conduction band minimum have been observed on different conditions. It has been shown that oxygen in silicon can restrain the interaction between Li and radiation-induced defects. Only when the concentration of Li is not far less than that of oxygen in silicon can lithium interact effectively with radiation-induced defects.     

直拉硅单晶原生漩涡缺陷的研究

本文用化学腐蚀方法,从含有漩涡缺陷的原生CZ硅单晶中分离出尺寸在1000—6000?间的氧沉淀,制成萃取复型样品,用TEM对氧沉淀作微区电子衍射分析。同时,观察硅薄膜中漩涡缺陷的TEM象,确定了二者的对应关系。结果表明,构成漩涡缺陷的氧沉淀主要是呈方形片的热液石英(keatite,silicak)及少量呈六角片的α方英石(α-cristobalite),沉淀片周边沿<110>方向,惯习面前者的为{100},后者的为{111}。样品的红外吸收光谱表明,方片状热液石英沉淀可能与1224cm^-1吸收峰相对应。 关键词：     

Deep level transient spectroscopy of hole traps in Zn-annealed ZnTe

Hole traps in Schottky barrier diodes of p-ZnTe that had previously been annealed in liquid Zn have been investigated using Deep Level Transient Spectroscopy (DLTS). Three traps have been investigated in 3etail and have activation energies of between E_v = 0.28 eV and E_v + 0.59 eV. All traps are assigned to acceptor defects because of their large capture cross sections for holes and one of these is tentatively assigned to a V_Zn native acceptor. From capacitance-temperature plots we deduce that Cu_Zn is the dominant shallow acceptor in as-grown material but after annealing the Cu_Zn concentration is reduced and a yet shallower acceptor, probably Li_Zn, predominates.     

Rydberg states of HCN observed by electron impact spectroscopy

The electron energy loss spectrum of HCN has been determined in the energy region 8–13.6 eV at impact energies of 100, 50 and 30 eV. It is shown that energy loss spectra of HCN at intermediate impact energies can be satisfactorily analysed unlike the diffuse unassigned optical absorption spectra that have previously been reported. Rydberg series have been assigned using term values and quantum defects together with ionization potentials obtained by photoelectron spectroscopy.     

Formation of defect density superlattices in binary compounds under nuclear irradiation

Manifestation of antisite defects in crystals under irradiation is studied. Calculations show that the concentration of such defects can reach high levels under typical irradiation intensities and temperatures. It is shown that buildup of antisite defects and interaction between them can result in instability of the system during irradiation with respect to spatially nonuniform perturbations. The instability should give rise to a periodic modulation of the density of antisite defects. The region of instability as a function of crystal parameters and irradiation has been obtained.     

正电子湮没谱和光致发光谱研究掺锌GaSb质子辐照缺陷

用正电子湮没谱和光致发光谱研究了质子辐照后掺锌GaSb中的缺陷.通过分析正电子的缺陷寿命τ₂及强度I₂的变化发现,在高能质子的辐照下产生了双空位缺陷V_GaV_Sb,可能同时产生了小的空位团.正电子平均寿命τ_av和S参数随着质子辐照剂量的变化也证明了这一结论.通过分析不同质子辐照剂量下掺锌GaS     

Electronic structure and resonant X-ray emission spectra of carbon shells of iron nanoparticles

The electronic structure of carbon shells of carbon encapsulated iron nanoparticles carbon encapsulated Fe@C has been studied by X-ray resonant emission and X-ray absorption spectroscopy. The recorded spectra have been compared to the density functional calculations of the electronic structure of graphene. It has been shown that an Fe@C carbon shell can be represented in the form of several graphene layers with Stone-Wales defects. The dispersion of energy bands of Fe@C has been examined using the measured C Kα resonant X-ray emission spectra.     

InP中深能级缺陷的产生与抑制现象

研究了原生和高温退火处理后非掺n型和半绝缘InP单晶材料中产生的缺陷.在磷气氛下退火后，n型和半绝缘InP单晶中均明显产生相当数量的深能级缺陷，而在磷化铁气氛下退火后，InP的缺陷数量明显减少.在退火过程中缺陷的产生与磷和铁的内扩散有直接关系.向内扩散的磷原子和铁原子占据晶格中铟位后，分别产生反位缺陷和铁深受主.实验结果表明，铁通过扩散充分占据了铟位，抑制了铟空位、磷反位等缺陷的形成，而磷气氛下退火后产生的缺陷有铟空位、磷反位等.对InP中的缺陷属性进行了分析. 关键词： 磷化铟 退火 缺陷