用深能级瞬态谱法测量GaAS MESFET中的深能级

本文介绍了用深能级瞬态谱(DLTS)法测量GaAs MESFET的深能级杂质和缺陷。在有源层中一般没有测到深能级杂质和缺陷,但在有源层与缓冲层界面附近测到了多个空穴陷阱和电子陷阱。其中空穴陷阱的能级有0.41eV、0.53eV、0.68eV、0.91eV;电子陷阱的能级有0.30eV、0.44eV、0.84eV。并对部分陷阱的性质作了初步的讨论。     

锗硅量子阱异质界面附近缺陷研究

用深能级瞬态谱（ＤＬＴＳ）研究了量子阱样品价中载流子的热发射和异质界面附近的深能级缺陷，得到Ｓｉ０．６７Ｇｅ０．３３／Ｓｉ单量子样品的能带偏移为０．２４ｅＶ．量子阱异质界面附近高浓度的深能级缺陷在样品的ＤＬＴＳ谱上形成一少于峰，该信号只有当测量的脉冲宽度足够大时才能检测到．对比不；司组分相同结构的多量子阱样品发现，组分大时异质界面的深能级缺陷浓度大，因此它可能是失配应变或位错引起的．相应的光致发光谱（ＰＬ）测试结果表明该深能级缺陷还会导致ＰＬ谱中合金层的带边激子峰的湮灭．     

硅中铂能级的DLTS研究

用深能级瞬态谱(DLTS)研究了铂在N型和P型硅中引入的能级.制备了p~+nn~+深结,p~+n和n~+p浅结,Au/n-Si和Ti/p-Si肖特基等五种掺铂样品.分析各种样品的测试结果得到:过去报道在p~+nn~+深结中测得的Ec—0.34eV能级并不存在于N型硅中,该DLTS谱峰来源于p~+nn~+结P型区内的空穴发射.     

电声子耦合对量子点非平衡输运的影响

电子-声子耦合显著影响半导体量子点和单分子晶体管的非平衡输运.在非平衡格林函数运动方程方法的框架内,通过改进电声子解耦,发现低温下量子点谱函数中声子伴带明显依赖于两边电极费米能级与重整后局域能级的相对位置,呈现电子-空穴对称性破缺.Kondo峰的声子伴带分为两类,分别与由电子或空穴组成的多体自旋单态相对应.当局域能级存在Zeeman分裂时,两类不同起源的Kondo声子伴带在自旋分辨的谱函数中可以相互区分.谱函数的这些特性也体现在非线性微分电导谱中.     

电声子耦合对量子点非平衡输运的影响

电子-声子耦合显著影响半导体量子点和单分子晶体管的非平衡输运.在非平衡格林函数运动方程方法的框架内,通过改进电声子解耦,发现低温下量子点谱函数中声子伴带明显依赖于两边电极费米能级与重整后局域能级的相对位置,呈现电子-空穴对称性破缺.Kondo峰的声子伴带分为两类,分别与由电子或空穴组成的多体自旋单态相对应.当局域能级存在Zeeman分裂时,两类不同起源的Kondo声子伴带在自旋分辨的谱函数中可以相互区分.谱函数的这些特性也体现在非线性微分电导谱中.     

电声子耦合对量子点非平衡输运的影响

电子-声子耦合显著影响半导体量子点和单分子晶体管的非平衡输运. 在非平衡格林函数运动方程方法的框架内，通过改进电声子解耦，发现低温下量子点谱函数中声子伴带明显依赖于两边电极费米能级与重整后局域能级的相对位置，呈现电子-空穴对称性破缺. Kondo峰的声子伴带分为两类，分别与由电子或空穴组成的多体自旋单态相对应. 当局域能级存在Zeeman分裂时，两类不同起源的Kondo声子伴带在自旋分辨的谱函数中可以相互区分. 谱函数的这些特性也体现在非线性微分电导谱中.     

InAs/GaAs量子点光致发光光谱多峰结构发光本质

研究了InAs/GaAs量子点光致发光光谱中出现的多峰结构.观察到随着激发功率的增加光谱中发光峰的数目逐渐增多并且部分发光峰的峰位随激发功率的增加向高能量方向移动.解释了各发光峰的来源并结合量子点能级结构的特点,计算了量子点中电子和空穴各子带间的能级间距.     

InAs/GaAs量子点光致发光光谱多峰结构发光本质

研究了InAs/GaAs量子点光致发光光谱中出现的多峰结构. 观察到随着激发功率的增加光谱中发光峰的数目逐渐增多并且部分发光峰的峰位随激发功率的增加向高能量方向移动. 解释了各发光峰的来源并结合量子点能级结构的特点,计算了量子点中电子和空穴各子带间的能级间距.     

Hg1—xCdxTe深缺陷能级研究

利用深能级瞬态谱(DLTS)研究了Hg_(1-x)Cd_xTe(x=0.4)p~+n光伏二极管中的缺陷能级.通过改变注入脉冲条件,获得2个电子陷阱和2个空穴陷阱,电子陷阱的能级位置分别为E(0.06)和E(0.15),空穴陷阱的能级位置分别为H(0.075)和H(0.29).这些深能级的浓度约为浅能级浓度的百分之几.通过改变注入脉冲的宽度,测量了这些能级的多子俘获截面,根据这些深能级的特征参数,估算了器件的少子寿命和零偏压的动态电阻与面积的乘积,并讨论了一些缺陷能级的本质.     

1nm i-AlN电子阻挡层对AlGaN-UV-LED性能的影响

采用有机金属化学气相沉积法,在1μm氮化铝/蓝宝石衬底上制备了不同结构的AlGaN基多量子阱结构的深紫外发光二极管,其禁带边发光峰位为264 nm。使用透射扫描电镜对器件的结构进行了表征,测试了器件的光学和电学性能。通过分析电致发光谱得出:在器件活性区域和p型AlGaN盖层之间插入1 nm i-AlN电子阻挡层的样品其位于320 nm处的寄生发光峰能被有效抑制,该杂质峰主要是由于电子溢出至p型盖层,与处于Mg相关的受主深能级上的空穴复合所致。此外,验证了该电子阻挡层对发光特性具有一定的改善效果。通过优化UV-LED结构以及合理设定外延层的厚度参数,可以使其出光功率提高一个量级。     

A novel technique of analyzing multiexponential transients for DLTS spectra

A new method is presented here to experimentally decompose capacitance transients into the appropriate components from the closely-spaced deep trap states. Using the Temperature Dependent Pulsewidth-DLTS (TDP-DLTS) technique, we show that two closely-spaced DX centers in Se-doped Al_0.6Ga_0.4As laser diodes can be successfully separated. We produce an Arrhenius plot for each individual component, which yield the thermal activation energies, emission rates and capture cross sections of the two closely spaced traps. Without any complicated mathematics or program, TDP-DLTS provides an accurate, convenient and consistent method for decomposing the multiexponential transients of DLTS spectra.     

瞬态C-V法测量AlGaAs:Si中DX中心的电离能(英文)

The thermal ionization energy ET of DX centers in AlxGa1-xAs and its dependence with the value of x and the pressure are very important for estab- lishing the model of DX centers. The conventional DLTS and Hall methods used to DX center measurement have some ambiguities in theoretical analysis and experiments and the values of ET determined are different with those methods. The new constant temperature transient C-V measurement is based on the fact that at low temperature both electron capture and emission rates of DX centers are very slow. During the transient C-V measurement, change; of bias voltages and capacitance measurements are completed in a time duration much shorter than the electron capture and emission time constants, therefore the electrons occupied on the DX centers are considered to be frozen. The density of DX centers, the distribution profile of electrons on DX centers in the depletion region of a Schottky diode at a constant reverse bias, and the density of free electrons in conduction band in the bulk and their temperature dependence have been measured.     

On the carrier emission from donor-related centres in GaAs1-xPx and AlxGa1-xAs

From an experimental study of the electron thermal emission and capture rates of Te-related centres, donor-related (DX) traps have been identified in GaAsP and GaAlAs compounds. It is shown that under thermal excitation nonexponential transient waveforms markedly deviate from theory. The relation of the nonexponential degree with alloy composition and junction electric field has been studied. In addition, optical activated transients, a model based on trap charge dependent emission and capture coefficients, and the drawbacks of Deep Level Transient Spectroscopy (DLTS) techniques to study DX centres are presented.     

Anomalous nanosecond transient component in a GaAs MODFETtechnology

Modulation-doped field-effect transistors (MODFETs) exhibit transient responses that contain a variety of time constants. The strongest transients observed in the microsecond range are known to be caused by the DX centers. MODFETs also suffer a transient that arises from a source different from that of the DX centers. Preliminary measured characteristics of the nanosecond transient are presented, its effects on circuit performance are described, and its possible origin is inferred     

Analysis of nonexponential deep-level current transients in schottky diodes fabricated on [1\bar 100] 6H-SiC00] 6H-SiC

A current deep-level transient spectroscopy (DLTS) system capable of recording an entire set of current transients was developed and used for characterization of deep levels in n-type 6H-SiC wafers grown in the [1 00] direction. The current transients were acquired in the time interval from 10⁻⁴ sec to 10 sec and temperature range from 100 K to 700 K. The current transients exhibited nonexponential behavior, which was related to closely spaced traps in the band gap. The logarithmic plot of the current transient was close to linear at most temperatures. Because the conventional approach based on exponential emission of electrons from discrete levels cannot describe the observed nonexponential behavior of current transients, the transients were fitted assuming continuous distribution of traps in the band gap. Theoretically calculated current transients assuming Gaussian distribution of trap centers in the band gap agree with the experimental data fairly well. The results of electrical measurements and theoretical fitting were explained based on a high density of defects in the investigated wafer that were revealed by chemical etching and related to stacking faults.     

AlGaAs∶Sn混晶中的两类类DX中心

在测得Al0.26Ga0.74As∶Sn混晶中两类类DX中心的电子热俘获势垒精细结构后,研究和确定了其相关的束缚能、晶格驰豫能和光离化能.采用第一原理赝势法的计算和分析结果表明,Sn施主杂质次近邻Al/Ga原子的不同局域组分所引起的Sn杂质及其最近邻As原子的不同晶格驰豫,是产生两类类DX中心能级精细结构的主要原因.     

Electron and Hole Capture Cross-Sections of Fe Acceptors in GaN:Fe Epitaxially Grown on Sapphire

Carrier trapping of Fe³⁺/Fe²⁺ deep acceptors in epitaxially grown GaN:Fe on sapphire was studied by time-resolved photoluminescence. For the investigated Fe doping levels on the order of 10¹⁸ cm⁻³, the luminescence decay times are strongly dependent on the Fe concentration, indicating that Fe centers act as predominant nonradiative recombination channels. Linear dependence of the decay time on the iron concentration allows estimation of the electron capture cross-section for the Fe³⁺ ions, which is equal to 1.9 × 10⁻¹⁵ cm². The upper bound for the cross-section of the hole capture of Fe²⁺ was evaluated as 1 × 10⁻¹⁵ cm².     

A detailed investigation of the D-X center and other trap levels in GaAs-AlxGa1-xAs modulation-doped heterostructures grown by molecular-beam epitaxy

We have re-examined the results and analysis of capacitance transient spectroscopy measurements made on modulation-doped heterostructures suitable for the fabrication of field-effect transistors. It is seen that conventional analysis of data can lead to erroneous results and a new model, which includes the contribution of the capacitance at the heterointerface, is presented. Most of the observed anomalous behavior related to trap emission can now be explained. Six main electron traps are present in single-layer AlxGa1-xAs, grown by molecular-beam epitaxy, and in device-quality GaAs-AlxGa1-xmodulation-doped heterostructures. These range in energy from 0.40 to 0.91 eV in thermal ionization energy. The well known D-X center in Si-doped AlxGal-xAs layers is composed of two closely spaced levels, DX1 and DX2, with ionization energies of 0.48 and 0.52 eV, respectively. At very low Si,doping levels, only DX2 is dominant, but at doping levels > 10¹⁸cm^-3, both DX1 and DX2 become comparable in concentration. The optical ionization properties of these levels were also measured and it is seen that the optical lineshapes differ markedly for the two centers. The peak photoionization cross sections occur at spectral energies of 1.25 and 1.38 eV for DX1 and DX2, respectively. The nature and symmetry of the centers have been studied by measurements on layers of different orientations.     

Deep level transient spectroscopy assessment of silicon contamination in AlGaAs layers grown by metalorganic vapor phase epitaxy

A systematic silicon contamination has been detected by deep level transient spectroscopy in undoped and n-type doped (Te, Se, Sn) AlGaAs layers, grown in two different metalorganic vapor phase epitaxy reactors. DX center generation by substitutional donors, with very specific capture and emission thermal barriers (fingerprints), is the key to unambiguously identifying their presence, with detection limits well below the standard secondary ion mass spectroscopy capability. We comment on the potential sources of Si contamination (most common in this epitaxial technique), and on the relevance of such contamination to interpreting correctly experimental data related to the microscopic structure of DX centers.     

Al_(0.35)Ga_(0.65)As中DX中心的俘获激活能(英文)

The capture, spectra in LPE-Ga0.35Al0.65As were studied. Two peaks of DX center is the capture spectra were obtained by a pulse with suitable duration, although there was one peak only in the emission spectra. It was possible thnt there were two deep levels about the different captures cross section and mar the emission rate. The unusual results of an emission activation energy of 0.31eV and a capture activation energy of 0.42eV were determined in the sample with NDX/Ns-1.7. Nonexponential single shot transient capacitance curves were imitated theoretically by using emission and capture equations for the high concentration of deep levels and by considering spreading factor of DX centers. Experimental curves were consistent with theoretical curves. The spreading factor of barrier was 40meV. Emission and capture activation energy were determined to be 0.3leV and 0.18eV, respectively.