掺铍GaAs量子阱的光致荧光

测量了掺铍的,阱宽约为10nm的GaAs量子阱在4.2K的光致荧光。掺杂浓度分别为1×10¹⁷和5×10¹⁸cm^-3。测量结果表明:对于无规掺杂,局域在阱中心的铍的状态密度与导带电子从n=1量子能级到阱中心中性铍的跃迁概率的乘积大于对应于介面铍的乘积。另外,实验结果也表明:当掺杂浓度升高时,由于带隙收缩的影响,阱中心铍的电离能减小。     

Optical properties of undoped,Be-doped,and Si-doped wurtzite-rich GaAs nanowires grown on Si substrates by molecular beam epitaxy

The photoluminescence (PL) of undoped, Si-doped, and Be-doped GaAs nanowires (NWs) grown on Si substrates by molecular beam epitaxy was investigated. PL peaks of the undoped and Be-doped NWs were observed at higher energies than the bandgap energy of GaAs bulk. According to X-ray diffraction analysis, the blue-shift is attributed to the wurtzite-rich GaAs NW structure. Impurity-related peaks were observed in the undoped NWs and the impurity was Si that diffused via interaction with the adatoms on the Si surface during the growth. A slight bandgap narrowing of the Be-doped GaAs NWs was observed from their PL spectra. The Si-doped NWs showed a very broad PL peak due to a larger density of Si-related defects originating from the heavy doping level. The dependence of the PL peaks of the NWs on temperature was also investigated.     

中子辐照高掺硅砷化镓的光致发光研究

研究了高掺硅的n型GaAs在中子辐照前后和150℃-500℃等时热退火以后的光致发光光谱。观察到在中子辐照后积分发光强度降低为辐照前的1/36。在退火温度超过250℃时,积分发光强度显著增长,当退火温度达400℃以上时,在带边峰的低能侧出现能量为1.35eV、1.30eV和1.26eV的发光峰。假设250℃退火阶段对应于较大的空位团分解为较小的空位团,400℃退火阶段对应于较小的空位团分解出VGa,可以较好地解释实验现象。     

Quantum transport in periodically δ-doped GaAs

The Shubnikov-de Haas spectra of GaAs samples with a periodical doping with Si were measured at 4.2 K using fields of 0–14 T. From the Shubnikov-de Haas spectrum the quantum mobilities associated with individual minibands were estimated for each sample. The sheet density of Si atoms in each doping plane was fixed at approximately 2.5 × 10¹² cm^?2 in all samples and the doping period was varied in the range 40–1000 Å. The quantum mobilities obtained experimentally are compared with theoretical calculations using the random phase approximation to describe the screened interaction between electrons and charged impurities. The theory describes qualitatively the results of the experiment, i.e. an increase of the quantum mobility with the index of the miniband, and a decrease in the mobility in all minibands when the doping period is made shorter (with a weak maximum at intermediate values of the doping period). Various possible improvements of the model are suggested.     

An ab initio-based approach to adsorption-desorption behavior of Si adatoms on GaAs(1 1 1)A-(2 × 2) surfaces

The adsorption-desorption behavior of Si adatoms on GaAs(1 1 1)A-(2 × 2) surfaces is investigated using our ab initio-based approach, in which adsorption and desorption behavior of Si adatoms is described by comparing the calculated desorption energy obtained by total-energy electronic-structure calculations with the chemical potential estimated by quantum statistical mechanics. We find that the Si adsorption at the Ga-vacancy site on the (2 × 2) surfaces with As adatoms occurs less than 1140-1590 K while the adsorption without As adatom does less than 630-900 K. The change in adsorption temperature of Si adatoms by As adatoms is due to self-surfactant effects of As adatoms: the promotion of the Si adsorption triggered by As adatoms is found to be interpreted in terms of the band-energy stabilization. Furthermore, the stable temperature range for Si adsorbed surfaces with As adatoms agrees with the experimental results. The obtained results provide a firm theoretical framework to clarify n-type doping processes during GaAs epitaxial growth.     

Energy levels in doped SiGe quantum well studied by admittance spectroscopy

SiGe/Si quantum wells (QWs) with different Boron doping concentrations were grown by molecular beam epitaxy (MBE) on p-type Si(1 0 0) substrate. The activation energies of the heavily holes in ground states of QWs, which correspond to the energy differences between the heavy hole ground states and Si valence band, were measured by admittance spectroscopy. It is found that the activation energy in a heavily doped QW increases with doping concentration, which can be understood by the band alignment changes due to the doping in the QWs. Also, it is found that the activation energy in a QW with a doping concentration of 2 × 10²⁰ cm⁻³ becomes larger after annealing at a temperature of 685 °C, which is attributed to more Boron atoms activation in the QW by annealing.     

DX<Superscript>−</Superscript> center formation in planar-doped GaAs:Si in strong electric fields

The kinetics of current decay and partial restoration in planar doped GaAs:Si due to the formation of DX^? centers in strong electric fields has been experimentally studied. The existence of thresholds with respect to the field strength and donor concentration is explained. A model of the DX^? center formation is proposed, which is based on the notions about variation of the depth and width of a potential well created by planar doping, caused by the redistribution of hot electrons between quantum confinement subbands. As a result, the energy level of DX^? centers, which is situated above the potential well depth in the absence of strong field, decreases and falls within the potential well. This makes possible the DX^? center formation, provided that hot electrons, occupying the resonance electron levels in the conduction band, simultaneously excite local vibrational modes.     

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species Si_Ga ⁺ and as shallow acceptor species Si_As ^-. The solubility of Si_As ^- is much lower than that of Si_Ga ⁺ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is Si_Ga ⁺ which will convert into Si_As ^- in accordance with their solubilities and that the point defect species governing the diffusion of Si_Ga ⁺ are triply-negatively-charged Ga vacancies V_Ga ^3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n⁺-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently. Received: 19 April 1999 / Accepted: 3 May 1999 / Published online: 4 August 1999     

Thermal interdiffusion in InGaAs/GaAs and GaAsSb/GaAs strained quantum wells as a function of doping density

We studied the thermal stability and interdiffusion of InGaAs/GaAs and GaAsSb/GaAs single quantum wells as a function of temperature for both Be and Si doping at various doping concentrations. The interdiffusion was monitored using the photoluminescence from the ground states of the valence- and conduction-band quantum wells. Using a Green's function method to solve the diffusion equation, assuming Fick's law behaviour, the evolution of the well shape during annealing was determined, and Schrödinger's equation was solved for this well shape to provide the ground-state energy levels of the system using the diffusion constant as the only fitting parameter. The validity of this model as applied to both systems is discussed.Strained Layer Structures Research Group.     

Generation mechanism and thermal stability of high carrier concentrations by KrF-excimer-laser doping of Si into GaAs

The generation mechanism and thermal stability of high carrier concentrations in GaAs formed by KrF-excimer-laser doping with Si using SiH₄ gas are investigated. The channeling Particle-Induced X-ray Emission (PIXE) analysis reveals that a high substitutional fraction of over 90% and preferential replacement of Si atoms on Ga sites result in the generation of carrier concentrations as high as 5×10¹⁹ cm^–3. In addition, the thermal stability of the doped regions is studied. The high carrier concentrations in a nonthermal equilibrium state return to a thermal equilibrium state by postannealing.Presented at LASERION'93, Munich, June 21–23, 1993     

Influence of laser fluence and dopant gas pressure on properties of photochemical doping of Si into GaAs using XeCl excimer Laser

Silicon doping into GaAs has been performed with the combination of pulsed XeCl excimer laser (wavelength: 308 nm) and silane gas (SiH₄). Sheet resistances and depth profiles of the Si-doped GaAs as the functions of laser fluence, the number of laser pulses and gas pressure have been measured in order to make clear the relation between properties of doped GaAs and irradiation conditions. The secondary ion mass spectroscopy (SIMS) has revealed that the depth of Si in GaAs is limited in such a very shallow region (30–110 nm) that might be controlled easily by irradiation conditions. The efficiency for carrier generation of Si in GaAs with laser fluence is discussed.     

Electrical characterization of defects introduced in n-GaAs by alpha and beta irradiation from radionuclides

We investigated defect production in n-type GaAs with two different free-carrier densities (4×10¹⁴ and 1×10¹⁶/cm³) by using particles liberated from radionuclides. ⁹⁰Sr and ²⁴¹Am were employed as beta and alpha sources, respectively. The results obtained for electron irradiation showed that the same set of primary defects can be produced by beta irradiation from the Sr source as by electrons produced in an accelerator. Similarly, the defects produced by alpha irradiation from the Am source closely resemble those introduced by alpha irradiation in a Van de Graaff accelerator. It was found that the relative concentrations of the primary defects in electron-irradiated GaAs are different to those in alpha-particle irradiated GaAs. Further, for the first time, an alpha irradiation induced defect which seems to be related to the doping concentration was observed in the 10¹⁶/cm³ Si doped GaAs. It is concluded that the use of radionuclides is an inexpensive and convenient method to introduce and to study radiation induced defects in semiconductors.     

Self-consistent tight-binding total energy calculations: Application to GaAs/Si and ZnSe/GaAs (100) interfaces

Self-consistent tight-binding total energy calculations are performed for various models of GaAs/Si and ZnSe/GaAs (100) interfaces. A graded GaAs/Si interface with the first monolayer on substrate having 1 As atom per 3 Si atoms followed by a second monolayer with 3 Ga atoms per 1 Si atom and continued with 2 bulk-like As and Ga monolayers is found to be structurally more stable than other interfaces. The instability of the abrupt interface is driven by elastic rather than electrostatic forces. Similar results are obtained for the ZnSe/GaAs (100) interface. The graded interface with Ga atoms exchanged against Zn atoms is found to be energetically most stable. Strong macroscopic electric fields are found in the surface and interface regions for both the GaAs/Si and ZnSe/GaAs interfaces.     

Probing charge carrier compensation in high energy ion irradiated III–V semiconductor by Raman spectroscopy and Hall measurements

Raman spectroscopy and Hall measurements have been carried out to investigate the differences in near‐surface charge carrier modulation in high energy (~100 MeV) silicon ion (Si⁸⁺) and oxygen ion (O⁷⁺) irradiated n‐GaAs. In the case of O ion irradiation, the observed decrease in carrier concentration with increase in ion fluence could be explained in the view of charge compensation by possible point defect trap centers, which can form because of elastic collisions of high energy ions with the target nuclei. In Si irradiated n‐GaAs one would expect the carrier compensation to occur at a fluence of 2.5 × 10¹³ ions/cm², if the same mechanism of acceptor state formation, as in case of O irradiation, is considered. However, we observe the charge compensation in this system at a fluence of 5 × 10¹² ions/cm². We discuss the role of the complex defect states, which are formed because of the interaction of the primary point defects, in determining carrier concentration in a Si irradiated n‐GaAs wafer. The above results are combined with the reported data from the literature for high energy silver ion irradiated n‐GaAs, in order to illustrate the effect of both electronic and nuclear energy loss on trap creation and charge compensation. Copyright © 2016 John Wiley & Sons, Ltd.     

掺杂浓度及掺杂层厚度对Si均匀掺杂的GaAs量子阱中电子态结构的影响

本文通过自洽地求解薛定鄂方程及泊松方程计算了在温度T=0, 有效质量近似下, Si均匀掺杂的GaAs/AlGaAs量子阱系统的电子态结构. 研究了掺杂浓度及掺杂层厚度对子带能量, 本征包络函数, 自洽势, 电子密度分布, 及费米能量的影响. 发现在给定掺杂浓度下, 子带能量随掺杂层厚度的增加单调递减, 自洽势的势阱变宽变浅, 电子密度分布变宽, 峰值变低; 在给定掺杂层厚度下, 随掺杂浓度的增加子带能量及费米能级单调递增, 自洽势阱变深变陡变窄, 电子密度分布的峰值变高, 集中在中心. 关键词： 掺杂 量子阱 电子结构 半导体GaAs     

Measurement of nonlinear absorption coefficients in GaAs, InP and Si by an optical pump THz probe technique

An optical pump terahertz (THz) probe method for measuring carrier mobility and multiphoton absorption coefficients in semiconductors is demonstrated. A THz probe pulse is used to detect the transient photoconductivity generated by an optical pump pulse. The change in transmission coefficient at THz frequencies due to a pump pulse with photon energy greater than the band gap energy is used to determine the sum of electron and hole mobilities. The weak nonlinear absorption of a pump pulse with photon energy less than the band gap energy produces an approximately uniform free carrier distribution. The THz transmission coefficient vs. pump fluence, and the mobility, are used in a bulk photoconductivity model to determine the multiphoton absorption coefficients. For GaAs, InP and Si we find two photon absorption coefficients at 1305 nm of 42.5 ± 11, 70 ± 18 and 3.3 ± 0.9 cm/GW, respectively. For GaAs and InP we determine three photon absorption coefficients at 2144 nm of 0.19 ± 0.07 and 0.22 ± 0.08 cm³/GW².     

Microscopic origin of the phenomenological equilibrium "Doping limit Rule" in n-type III-V semiconductors

The highest equilibrium free-carrier doping concentration possible in a given material is limited by the "pinning energy" which shows a remarkable universal alignment in each class of semiconductors. Our first-principles total energy calculations reveal that equilibrium n-type doping is ultimately limited by the spontaneous formation of close-shell acceptor defects: the (3-)-charged cation vacancy in AlN, GaN, InP, and GaAs and the (1-)-charged DX center in AlAs, AlP, and GaP. This explains the alignment of the pinning energies and predicts the maximum equilibrium doping levels in different materials.     

Self-organized in-plane incorporation of Si atoms in GaAs by molecular beam epitaxy

The preferential attachment of Si atoms at misorientation steps on vicinal GaAs(001) surfaces has been studied by RHEED. By analysing the time evolution of the specular beam intensity and the change in surface reconstruction during Si deposition we show that a self-organized Si incorporation along the step edges takes place. The observed (3×2) structure is due to an ordered array of dimerized Si atoms with missing dimer rows. Taking into account the structure of the (3×2) unit mesh and its orientation with respect to the As-terminated or Ga-terminated steps, a characteristic minimum in the RHEED intensity recording corresponds to the number of Ga step-edge sites. Since the preferential path for Ga as well as for Si adatom diffusion is along the [110] direction, the critical terrace width for wirelike Si attachment is much larger for a misorientation toward (111)As than for a misorientation toward (111)Ga. Despite the high local impurity concentration, the Si-modified surface can be overgrown with GaAs without adverse effects on the growth front. This is promising for the fabrication of doping wires.     

Distribution of carriers in gradient-doping transmission-mode GaAs photocathodes grown by molecular beam epitaxy

The gradient-doping structure is first applied to prepare the transmission-mode GaAs photocathode and the integral sensitivity of the sealed image tube achieves 1420~μ A/lm. This paper studies the inner carrier concentration distribution of the gradient-doping transmission-mode GaAs photocathode after molecular beam epitaxy (MBE) growth using the electrochemical capacitance-voltage profiling. The results show that an ideal gradient-doping structure can be obtained by using MBE growth. The total band-bending energy in the gradient-doping GaAs active-layer with doping concentration ranging from 1× 10^19~cm^-3 to 1×10^18~cm^-3 is calculated to be 46.3 meV, which helps to improve the photoexcited electrons movement toward surface for the thin epilayer. In addition, by analysis of the band offsets, it is found that the worse carrier concentration discrepancy between GaAs and GaAlAs causes a lower back interface electron potential barrier which decreases the amount of high-energy photoelectrons and affects the short-wave response.     

Magneto-optical study of shallow donors in transmutation-doped GaAs

Lineshapes and peak positions of 1s→2p^?1, donor transitions in epitaxial GaAs samples of relatively low compensation have been studied as functions of magnetic field by use of photoconductivity measurements. Some of these samples were produced by transmutation doping using thermal neutrons—a method which is useful for the controlled introduction of donor impurities in GaAs. Two new effects, tentatively attributed to van der Waals interactions between neutral donor atoms, are observed: (1) although both Se and Ge donors are introduced by thermal neutron transmutation, the Se line is much broader than the Ge line, and (2) deviations from isolated-donor behavior occur in the magnetic field dependence of the chemical shift of the shallowest donor present. The separation of lines from two deeper donors, Ge and Si, verified the simple phenomenological theory of the magnetic field dependence of central cell corrections of isolated donors up to at least 10T.