InP中皮秒快速现象

利用测量瞬态反射谱的方法，探索了掺硫、铁、锌以及非掺杂的ＩｎＰ中载流子寿命，观察到非掺杂ＩｎＰ中载流子寿命最长约６０ｐｓ，掺锌ＩｎＰ中载流子寿命３８ｐｓ居中，掺硫和掺铁的寿命最短约１ｐｓ掺硫、铁和锌的ＩｎＰ中载流子寿命下降，是由于掺杂引入了复合中心，这一结果已被喇曼光谱所证实。     

The minority carrier lifetime in doped and undoped p-type Hg0.78Cd0.22Te liquid phase epitaxy films

This paper will describe: (1) the first comparative study of recombination mechanisms between doped and undoped p-type Hg_1-xCd_xTe liquid phase epitaxy films with an x value of about 0.22, and (2) the first determination of τ_A7 ⁱ/τ_A1 ⁱ ratio by lifetime’s dependence on both carrier concentration and temperature. The doped films were either copper- or gold-doped with the carrier concentration ranging from 2 x 10¹⁵ to 1.5 x 10¹⁷ cm^-3, and the lifetime varied from 2 μs to 8 ns. The undoped (Hg-vacancy) films had a carrier concentration range between 3 x 10¹⁵ and 8 x 10¹⁶ cm^-3, and the lifetime changed from 150 to 3 ns. It was found that for the same carrier concentration, the doped films had lifetimes several times longer than those of the undoped films, limited mostly by Auger 7 and radiative recombination processes. The ineffectiveness of Shockley-Read-Hall (SRH) recombination process in the doped films was also demonstrated in lifetime vs temperature curves. The important ratio of intrinsic Auger 7 lifetime to intrinsic Auger 1 lifetime, τ_A7 ⁱ/τ_A1 ⁱ, was determined to be about 20 from fitting both concentration and temperature curves. The reduction of minority carrier lifetime in undoped films can be explained by an effective SRH recombination center associated with the Hg vacancy. Indeed, a donor-like SRH recombination center located at midgap (E_v+60 meV) with a capture cross section for minority carriers much larger than that for majority carriers was deduced from fitting lifetime vs temperature curves of undoped films.     

Epitaxial GaP by a semi-sealed dip process for high efficiency red LED's

A semi-sealed dip process has been used to grow Zn-O doped GaP layers for high efficiency red LED's. A close fitting floating quartz plug is used to prevent volatilization of Zn, Ga₂O, and GaP during saturation. Double epitaxial layers with efficiencies as high as 8. 0% have been grown by this process.     

A comparison of gamma-induced degradation and forward bias-induced degradation in GaP:Zn,0 LEDs

Both the effects of gamma irradiation and high-current forward bias on GaP:Zn,0 light emitting diodes (LEDs) have been studied by measuring constant current 76K electroluminescence (EL) spectra below 1000 nm, total light output at room temperature, and capacitance transients using the technique of deep level transient spectroscopy (DLTS). The LEDs were divided into two sets; a control set which was subjected only to forward bias, and a set exposed to gamma irradiation and forward bias. The results indicate that gamma-induced light output degradation occurs through a different mechanism than forward bias-induced degradation of the control LEDs. Gamma irradiation, which has no effect on the Zn-O concentration, degrades the light output through the introduction of competing non-radiative recombination centers which reduce the minority carrier lifetime. In contrast, forward bias-induced light output degradation is primarily due to a reduction in Zn-O concentration through the apparent recombination-enhanced interaction of Zn-O centers with impurities rather than defects. This work was supported in part by the Air Force Weapons Laboratory (AFWL) Kirtland AFB, Albuquerque, NM under P. O. 77-027, and in part by the U. S. Department of Energy (DOE) under contract number AT(29-1)789.     

Measurement of minority carrier lifetime and diffusion length in silicon epitaxial layers by means of the photocurrent technique

A new method for the determination of minority carrier lifetime and diffusion length in thin silicon epitaxial layers was developed. Using a transparent MIS structure the surface recombination velocity was reduced below 25 cm/s. This method makes possible to determine minority carrier lifetime and also diffusion length much greater than the thickness of the epitaxial layer.     

SEM cathodoluminescence studies of dislocation recombination in GaP

Single dislocations in epitaxial layers of GaP have been investigated using high resolution scanning electron microscope (SEM) cathodoluminescence (CL) techniques. The minority carrier lifetime was measured from the CL decay time constant, and impurity concentrations were assessed from a detailed analysis of the CL spectra. The minority carrier lifetime reduction at single dislocations varied between 10 and 40% depending on doping and growth procedure, decreasing to zero at approximately one diffusion length from the dislocation. A model based on recombination at an internal cylindrical surface did not adequately fit the experimental results, and it was therefore assumed that recombination occurred at a Cottrell atmosphere of impurities or defects surrounding the dislocation. Evidence to support such behaviour was obtained from CL spectra, which showed aggregation of nitrogen and a centre, probably a vacancy-donor complex, at 1.72 eV around dislocations. The close similarity between bulk and dislocation temperature dependence of lifetime suggests that the bulk recombination centre may be aggregating around dislocations.     

Wide-bandgap epitaxial heterojunction windows for silicon solarcells

It is shown that the efficiency of a solar cell can be improved if minority carriers are confined by use of a wide-bandgap heterojunction window. For silicon (lattice constant a=5.43 Å), nearly lattice-matched wide-bandgap materials are ZnS (a=5.41 Å) and GaP (a=5.45 Å). Isotype n-n heterojunctions of both ZnS/Si and GaP/Si were grown on silicon n-p homojunction solar cells. Successful deposition processes used were metalorganic chemical vapor deposition (MO-CVD) for GaP and ZnS, and vacuum evaporation of ZnS. Planar (100) and (111) and texture-etched ((111) faceted) surfaces were used. A decrease in minority-carrier surface recombination compared to a bare surface was seen from increased short-wavelength spectral response, increased open-circuit voltage, and reduced dark saturation current, with no degradation of the minority carrier diffusion length     

Electrical and optical properties of lodine doped CdZnTe layers grown by metalorganic vapor phase epitaxy

Electrical and photoluminescence properties of iodine doped CdZnTe (CZT) layers grown by metalorganic vapor phase epitaxy have been studied. Doped layers showed an n-type conductivity from the Zn composition x=0 (CdTe) to 0.07. Above x=0.07, resistivities of doped layers increased steeply up to 10⁶ Ω-cm. Resistivities of doped CZT layers were higher than those of undoped layers above x=0.6. Photoluminescence intensity of doped layers increased compared to undoped layers. Doped CdTe and ZnTe layers showed neutral donor bound exciton emission lines at the exciton related region. Also, these layers showed an increase in emission intensity at the donor acceptor pair recombination bands. Sharp emission lines were observed in doped CZT layers at around 1.49 eV. These emission lines were considered to be originated from GaAs substrates which were optically excited by the intense emission from doped CZT layers.     

双面抛光单晶硅片少子扩散长度的测量

本文改进了常规表面光电压测试少子扩散长度法,采用环形下电极消除了薄样品背面光电压信号对测量结果的影响;应用阻尼最小二乘法数据处理原理对实验数据进行“曲线拟合”,求出少子扩散长度和背面表面复合速度。本文讨论了该方法的测量范围。     

Minority carrier lifetime in doped and undoped epitaxially grown n-type CdxHg1−xTe

The performance of infrared detectors made from Cd_xHg_1-xTe (CMT) is related to the lifetime of minority carriers in the material. Both photoconductive and photovoltaic devices require long lifetimes for high performance. This paper compares lifetime measurements on epitaxially grown CMT layers which have been isothermally annealed to minimize the vacancy concentration and are n-type due to native defects, residual impurities, or deliberately added dopants. Layers grown by liquid phase epitaxy (LPE), metalorganic vapor phase epitaxy (MOVPE), and molecular beam epitaxy (MBE) have been considered, in all cases the same measurement system was used under the same low injection conditions. All layers were of compositions required for operation in the 8 to 14 μm wavelength range. Comparisons have been made between undoped and indium doped LPE layers and undoped and iodine doped MOVPE layers. It was hoped that a deliberately introduced donor impurity would give better control of the n-type properties. The effect of passivation on the measurement of lifetime has also been considered, the results showing that a surface with a native oxide is required to obtain the true bulk lifetime as has been seen previously for bulk material.     

Carrier recombination at dislocations in epitaxial gallium phosphide layers

Recombination at dislocations in epitaxial layers of GaP is studied by measuring the minority carrier lifetime around single dislocations. Dislocation lines, introduced by means of plastic deformation at a temperature of about 650°C, appear to be less efficient non-radiative recombination centres than the grown-in dislocations. The recombination efficiency of dislocations is significantly increased by the presence of impurities of different metals. Annealing at a temperature of 800°C decreases the lifetime by a factor of 2, probably due to the production of P-vacancies. Lifetime measurements in annealed samples and in as-grown etched by steps LPE and VPE layers show that the recombination efficiency of dislocations follows the P-vacancy and donor doping concentration. Taking the results as a whole, together with the temperature dependence of lifetime, we suggest that the enhanced non-radiative recombination at dislocations in GaP is due to a Cottrell atmosphere of S-donor/P-vacancy complexes around the dislocations (i.e. traps similar to those which limit the bulk lifetime) rather than due to the core structure of the dislocation.     

半导体单晶材料的表面光伏效应

本文报导了测量半导体单晶材料(Si、GaAs、GaP、InP)的表面光伏谱和少子扩散长度,以及用微型计算机进行曲线拟合计算出材料的掺杂浓度、载流子迁移率、表面势垒宽度和表面势垒边界的界面复合速度等参数;得到的掺杂浓度与霍尔方法的测量值做了对比;本文还讨论了曲线拟合计算结果的可靠性和准确性.     

A study of the effect of ultraviolet (UV) and vacuum ultraviolet (VUV) photons on the minority carrier lifetime of single crystal silicon processed by rapid thermal and rapid photothermal processing

Minority carrier lifetime is an efficient indicator of defect levels present in the starting material as well as process and equipment induced defects. By employing rapid thermal processing (RTP) and rapid photothermal processing (RPP) as the thermal processing techniques, we have studied the effect of ultraviolet (UV) and vacuum ultraviolet (VUV) photons on the bulk minority carrier lifetime of phosphorous doped and undoped single crystal silicon wafers. For both diffused and undiffused wafers, we have observed an enhancement in the minority carrier lifetime when UV and VUV photons are used in conjunction with the samples processed without the use of UV and VUV photons. The effect of ramp rates on the minority carrier lifetime and the significance of optimized thermal cycles have also been studied in this paper. A possible explanation based on the dependence of diffusion coefficient on the photo spectrum of light source is also given in this paper.     

Degradation of GaP:N LEDs

The degradation of light output with operating time has been studied for nitrogen doped GaP light emitting diodes fabricated from vapor phase epitaxial material. The degradation is found to saturate at a non-zero value of efficiency. The process is characterized in terms of a degradation rate constant and the saturation value of efficiency. The rate is found to be a strong function of current density during operation and to a lesser degree materials parameters such as dislocation density. The saturation value appears to be independent of these parameters. The degradation is specifically associated with a decrease in the minority carrier lifetime in the p-side of these diffused LEDs. A model for the generation of non-radiative recombination centers which describes the degradation process quantitatively is presented.     

Electrochemical capacitance voltage profiling of the narrow band gap semiconductor InAs

InAs is a narrow band gap compound semiconductor with potential applications in infra-red detectors and high speed transistors. In order to facilitate device design using this material, it is essential that carrier concentration profiles be accurately known. Capacitance-voltage (CV) profiling is often employed for this purpose. Due to surface Fermi level pinning, it is difficult to form metal Schottky contacts to InAs layers, making conventional CV profiling difficult. Electro-chemical CV (ECV) measurements have been successfully performed on InAs epilayers grown by molecular beam epitaxy on GaP. A solution of 0.2 M EDTA with 0.2M NaOH and 10–20% by volume of ethylenediamine acts both as an etchant and as a Schottky contact to InAs. The profiles obtained for undoped InAs layers were compared to Hall effect data, and showed good agreement. ECV profiling of thick layers with p- and n-type doped regions is also demonstrated.     

Electron beam-induced current investigation of GaN Schottky diode

In this article, we report the electron beam-induced current (EBIC) measurements in a GaN Schottky diode performed in the line-scan configuration. A theoretical model with an extended generation source was used to accurately extract some minority carrier transport properties of the unintentionally doped n-GaN layer. The minority hole diffusion length is found to increase from ∼0.35 μm near the junction to ∼1.74 μm at the bulk regions. This change is attributed to an increase of the carrier lifetime caused by the polarization effects, which are preponderant in this component. For depth distances exceeding 0.65 μm, it is shown that the measured current is produced by the reabsorption recombination radiation process. This corresponds to an absorption coefficient of 0.178 μm⁻¹, in good agreement with the optical absorption measurement.     

闭管扩散Zn对InP表面性质的影响

利用闭管扩散方法以Zn3P2为扩散源，在不同扩散温度和扩散时间下对非故意掺杂InP (100）晶片进行扩散. 用电化学C-V法（ECV）和二次离子质谱法(SIMS)分别测出了空穴浓度和Zn的浓度随深度的分布曲线. 结果表明扩散后InP表面空穴和Zn的浓度在扩散结附近突然下降，InP表面空穴浓度主要取决于扩散温度，扩散深度随着扩散时间的增长而变大，InP表面Zn浓度一般比空穴浓度高一个数量级. 另外对扩散后的样品进行光致发光（PL) 测试，表明在保证表面载流子浓度的同时，适当降低扩散温度和增加扩散时间能减小对InP表面性质的影响.     

非故意掺杂吸收层InP/InGaAs异质结探测器研究

为了获得低噪声铟镓砷（InGaAs）焦平面,需要采用高质量的非故意掺杂InGaAs（u-InGaAs）吸收层进行探测器的制备。采用闭管扩散方式,实现了Zn元素在u-InGaAs吸收层晶格匹配InP/In_0.53Ga_0.47As异质结构材料中的P型掺杂,利用扫描电容显微技术(SCM)对Zn在材料中的扩散过程进行了研究,结果表明,随着扩散温度和时间增加,p-n结结深显著增加,u-InGaAs吸收层材料的扩散界面相比较高吸收层浓度材料（5×1016 cm?3）趋于缓变。根据实验结果计算了530 ℃下Zn在InP中的扩散系数为1.27×10?12 cm2/s。采用微波光电导衰退法(μ-PCD)提取了InGaAs吸收层的少子寿命为5.2 μs。采用激光诱导电流技术(LBIC)研究了室温下u-InGaAs吸收层器件的光响应分布,结果表明:有效光敏面积显著增大,对实验数据的拟合求出了少子扩散长度L_D为63 μm,与理论计算基本一致。采用u-InGaAs吸收层研制的器件在室温(296 K)下暗电流密度为7.9 nA/cm2,变温测试得到激活能E_a为0.66 eV,通过拟合器件的暗电流成分,得到器件的吸收层少子寿命τ_p约为5.11 μs,与微波光电导衰退法测得的少子寿命基本一致。     

Effects of S,Si, or Fe dopants on the diffusion of Zn in InP during MOCVD

Diffusion of Zn in InP during growth of InP epitaxial layers has been investigated in layer structures consisting of Zn-InP epilayers grown on S-InP and Fe-InP substrates, and on undoped InP epilayers. The layers were grown by metalorganic chemical vapour deposition (MOCVD) atT = 625° C andP = 75 Torr. Dopant diffusion profiles were measured by secondary ion mass spectrometry (SIMS). At sufficiently high Zn doping levels ([Zn] ≥8 × 10¹⁷ cm⁻³) diffusion into S-InP substrates took place, with accumulation of Zn in the substrate at a concentration similar to [S]. Diffusion into undoped InP epilayers produced a diffusion tail at low [Zn] levels, probably associated with interstitial Zn diffusion. For diffusion into Fe-InP, this low level diffusion produced a region of constant Zn concentration at [Zn] ≈ 3 × 10¹⁶ cm⁻³, due to kick-out of the original Fe species from substitutional sites. We also investigated diffusion out of (Zn, Si) codoped InP epilayers grown on Fe-InP substates. The SIMS profiles were characterised by a sharp decrease in [Zn] at the epilayer-substrate interface; the magnitude of this decrease corresponded to that of the Si donor level in the epilayer. For [Si] ≫ [Zn] in the epilayer no Zn diffusion was observed; Hall measurements indicated that the donor and acceptor species in those samples were electrically active. All these results are consistent with the presence of donor-acceptor interactions in InP, resulting in the formation of ionised donor-acceptor pairs which are immobile, and do not contribute to the diffusion process.     

Separation of local bulk and surface recombination in crystalline silicon from luminescence reabsorption

Spontaneous photoemission of crystalline silicon provides information on excess charge carrier density and thereby on electronic properties such as charge carrier recombination lifetime and series resistance. This paper is dedicated to separating bulk recombination from surface recombination in silicon solar cells and wafers by exploiting reabsorption of spontaneously emitted photons. The approach is based on a comparison between luminescence images acquired with different optical short pass filters and a comprehensive mathematical model. An algorithm to separate both front and back surface recombination velocities and minority carrier diffusion length from photoluminescence (PL) images on silicon wafers is introduced. This algorithm can likewise be used to simultaneously determine back surface recombination velocity and minority carrier diffusion length in the base of a standard crystalline silicon solar cell from electroluminescence (EL) images. The proposed method is successfully tested experimentally. Copyright © 2009 John Wiley & Sons, Ltd.