Shallow acceptor luminescence in GaAs grown by liquid phase epitaxy

Two pairs of photoluminescence (PL) emission bands between 1.494 and 1.480 eV have been observed at 4.2°K from high purity, undoped GaAs layers grown by liquid phase epitaxy. The PL emission from doped layers grown after incremental Si additions to a single parent melt suggests that Si acceptors are responsible for the lower energy pair of bands near 1.484 eV. The identity of the acceptor species responsible for the higher energy pair near 1.493 eV is presently unknown.     

High resistivity layers of GaAs grown by liquid phase epitaxy

The preparation of high-resistivity undoped GaAs layers is described. The layers were epitaxially grown from the liquid phase on semi-insulating GaAs substrates. Up to 10⁶ Ωcm in resistivity were obtained. The layers are highly compensated. Their temperature behaviour resembles that of Cr-doped semi-insulating bulk material. Additionally it is reported on the doping effect of Cr, Fe, Co, and Ni in the liquid phase epitaxy.     

The critical thickness of silicon-germanium layers grown by liquid phase epitaxy

Silicon-germanium layers are grown from metallic solution on (100) and (111) silicon substrates. On (111) Si, coherently strained dislocation-free SiGe layers are obtained with thicknesses larger than predicted by the current models of misfit-induced strain relaxation. A comprehensive characterisation by imaging, diffraction, and analytical electron microscopy techniques is carried out to determine the critical thickness, study the onset of plastic relaxation, and explain the particular growth mechanisms leading to an unexpectedly high thickness of elastically strained SiGe layers. A vertical Ge concentration gradient and the formation of step edges on the layers, where lateral strain relaxes locally, explain the high critical thickness. The model of Matthews and Blakeslee is modified in order to match the experimental observations for solution-grown SiGe layers. Received: 29 July 1999 / Accepted: 29 July 1999 / Published online: 27 October 1999     

Defects in Ce-doped LuAG and YAG scintillation layers grown by liquid phase epitaxy

The single crystalline Lu₃Al₅O₁₂ (LuAG) and Y₃Al₅O₁₂ (YAG) garnet layers doped by Ce³⁺ ions were grown by the liquid phase epitaxy from the flux. The effect of the flux composition, growth conditions, and substrate polishing on the layer morphology, creation of defects, and on optical and emission properties of layers was studied. The defects typical of the epitaxial growth are discussed.     

Dislocation generation in silicon grown laterally over SiO2 by liquid phase epitaxy

Epitaxial lateral overgrowth (ELO) on thermally oxidized and patterned (111) Si is effected by liquid phase epitaxy (LPE). It produces Si layers spreading out on the amorphous SiO₂ which are either perfectly grown defect-free or, coexisting, defective layers containing dislocations. High voltage electron microscopy of the defective layers reveals regular arrangements of the dislocations which result from glide and multiplication processes governed by the elastic interactions between the dislocations. The nucleation of the first dislocations during the ELO process is attributed to a slight warping of the substrates. A corresponding bending of the epitaxial layer induces mechanical stress, which may exceed the critical value at the oxide edges of the seeding windows where the first dislocations nucleate. The characteristics of the dislocation arrangements and lattice imaging results support this model. Suggestions are made for ways to reduce stress and, thus, avoid dislocation formation.     

Near infrared photoluminescence observed in dilute GaSbBi alloys grown by liquid phase epitaxy

We report the first observation of photoluminescence (PL) from the dilute bismide alloy GaSbBi. Epitaxial layers are grown by liquid phase epitaxy technique onto GaSb (1 0 0) substrates and PL is obtained in the near infrared spectral range (λ ∼ 1.6 μm). Incorporation of 0.2, 0.3 and 0.4 at% Bi to the layer results in a decrease of band gap energy up to 40 meV as well as an increase of luminescence from the sample. Structural analysis confirms the successful incorporation of Bi consistent with an increase in lattice parameter. Raman spectroscopy measurements indicate vibrational modes due to GaBi as well as to free Bi atoms residing at interstitial spaces.     

变温吸收谱研究液相外延碲镉汞浅能级

利用变温吸收谱(11—300K)对非故意掺杂液相外延Hg_1-xCd_xTe进行研究,对吸收边在低温区间(<70K)出现的约7—20meV反常移动现象进行了分析.结果表明该现象是由材料中Hg空位作为受主能级存在而形成的,红移幅度与样品组分/载流子浓度有关.据此估算Hg空位大致位于价带上方约20meV,与Hg空位形成浅受主能级的经验公式计算结果基本符合.该结果可以解释由传统吸收谱方法确定材料禁带宽度略高于材料实际光电响应截止能量值的现象. 关键词： 碲镉汞 液相外延 汞空位 反常吸收     

Infrared absorption and Raman spectroscopy studies of InSbBi layers grown by liquid phase epitaxy

We report on the results of optical absorption and Raman spectroscopy measurements on InSbBi layers grown by liquid phase technique. A maximum Bi content of 0.4 at.%, as measured by energy dispersive X-ray (EDX) technique, is used in the experiments. Optical absorption measurements made on the samples indicate a room temperature energy band gap reduction up to about 6 meV with respect to undoped InSb layers grown by the same technique. Bi content calculated from this band gap reduction agrees with that obtained from EDX. A weak peak obtained at 152 cm^?1 in the Raman spectrum of the material is identified with the longitudinal optical phonon mode of InBi. Further a mode at 140 cm^?1 is observed due to isolated Bi atoms at the interstitial sites.     

Ion milling-assisted study of defect structure of HgCdTe films grown by liquid phase epitaxy

Ion milling, as a tool for “stirring” defects in HgCdTe by injecting high concentration of interstitial mercury atoms, was used for studying films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The films appeared to have very low residual donor concentration (∼10¹⁴ cm⁻³), yet, similar to the material grown by molecular beam epitaxy, contained Te-related neutral defects, which the milling activated electrically. It is shown that ion milling has a stronger effect on HgCdTe defect structure than thermal treatment, and yet eventually brings the material to an “equilibrium” state with defect concentration lower than that after low-temperature annealing.     

Raman scattering of Zn doped CuGaS2 layers grown by vapor phase epitaxy

Raman spectra for non-site-selectively and site-selectively Zn-doped CuGaS₂ layers grown by vapor phase epitaxy (VPE) were investigated. Although an appearance of characteristic Raman line(s) related with the doped Zn atom was not seen, an enhancement of the Raman intensity ratio of the highest LO mode to the A₁ mode (I_LO/I_A1) was observed. The site-selectively Zn-doped layers with p-type conductivity exhibited larger I_LO/I_A1 ratio compared to those with n-type conductivity. The observed correlation between the I_LO/I_A1 ratio and the peak energy of the photoluminescence characteristic for Zn-doped p-type samples (L emission) suggests that the enhancement of I_LO/I_A1 is due to the increase of Zn atom substituting Ga site (Zn_Ga) which is acting as an acceptor.     

Surface morphology of highly mismatched InSb films grown on GaAs substrates by molecular beam epitaxy

InSb films on GaAs(001) substrates with and without GaAs buffer layer have been grown by molecular beam epitaxy. Rather than surface undulations, aligned ripples and pyramidal hillocks along the orthogonal 〈110〉 directions were observed on the surface of InSb films. Both the preferential growth and the termination of ripples were proved to be related to strain‐driven mass transport. A model was proposed to elucidate the formation of the hillocks, which are more efficient to relax strain than ripples. Due to the strain relaxation through hillocks with small bases predominantly, the surfaces of the InSb films grown without a GaAs buffer layer are smoother than those of films grown with a GaAs buffer layer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

MOS transistors with epitaxial Si,laterally grown over SiO2 by liquid phase epitaxy

We describe the first MOS transistors fabricated in silicon-on-insulator layers, obtained by liquid phase epitaxial lateral overgrowth of Si over SiO₂. Growth is performed around 930°–920° C using indium as a solvent. The layers are therefore p-type and have a doping of 4·10¹⁶ cm^–3. Electron mobilities of 540 cm²/Vs are obtained in the inversion channel; the threshold voltage of transistors with a gate length of 14.1 m is 510 mV. Our data demonstrate the applicability of liquid-phase epitaxial Si grown over oxidized Si for future use in three-dimensional integrated-device processing.     

EPR measurement on Er-doped InP grown by organometallic vapor phase epitaxy

We have performed X-band ESR measurements on InP:Er epitaxial layers grown by organometallic vapor phase epitaxy, which were grown at the substrate temperatures of 530°C (sample A) and 580°C (sample B). Sample A shows a slightly anisotropic resonance aroundg = 6 with hyperfine structure due to the¹⁶⁷Er (I = 7/2) isotope at 3 K. This result is similar to the result for Erdoped bulk InP and it indicates that Er³⁺ ions are located in In tetrahedral sites. On the other hand, we do not see such a resonance for sample B, suggesting that the local symmetry of Er in sample B is different from sample A. The difference between samples A and B is consistent with the fluorescence-detected extended X-ray absorption fine structure results that the coordination number of Er depends on the growth temperature.     

Scintillation efficiency and X-ray imaging with the RE-Doped LuAG thin films grown by liquid phase epitaxy

Very thin scintillator imaging plates have recently become of great interest. In high resolution X-ray radiography, very thin scintillator layers of about 5–20 μm are used to achieve 2D-spatial resolutions below 1 μm. Thin screens can be prepared by mechanical polishing from single crystals or by epitaxial growth on single-crystal substrates using the Liquid Phase Epitaxy technique (LPE). Other types of screens (e.g. deposited powder) do no reach required spatial resolutions. This work compares LPE-grown YAG and LuAG scintillator films doped with different rare earth ions (Cerium, Terbium and Europium). Two different fluxes were used in the LPE growth procedure. These LPE films are compared to YAG:Ce and LuAG:Ce screens made from bulk single crystals. Relative light yield was detected by a highly sensitive CCD camera. Scintillator screens were excited by a micro-focus X-ray source and the generated light was gathered by the CCD camera’s optical system. Scintillator 2D-homogeneity is examined in an X-ray imaging setup also using the CCD camera.     

Porous AlN films grown on C-face SiC by hydride vapor phase epitaxy

We report the growth of porous AlN films on C-face SiC substrates by hydride vapor phase epitaxy (HVPE). The influences of growth condition on surface morphology, residual strain and crystalline quality of AlN films have been investigated. With the increase of the V/III ratio, the growth mode of AlN grown on C-face 6H-SiC substrates changes from step-flow to pit-hole morphology. Atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman analysis show that cracks appear due to tensile stress in the films with the lowest V/III ratio and the highest V/III ratio with a thickness of about 3 μm. In contrast, under the medium V/III ratio growth condition, the porous film can be obtained. Even when the thickness of the porous AlN film is further increased to 8 μm, the film remains porous and crack-free, and the crystal quality is improved.     

X-ray sensitivity of Cd0.9Zn0.1Te detectors

The X-ray sensitivity of Cd_0.9Zn_0.1Te detectors as a function of the effective X-ray energy and bias voltage is studied. It is shown that the sensitivity grows with effective X-ray energy and much more significantly with bias voltage. The sensitivity depends on the angle the X-ray beam makes with an electric field in the detector. In the energy range 28–72 keV, the sensitivity is the highest when the X-ray beam is normal to the electric field in the detector.     

Cd0.9Zn0.1Te晶体的Cd气氛扩散热处理研究

将生长得到的Cd0.9Zn0.1Te晶体在Cd气氛下及不同的温度条件下进行了退火处理. 借助已建立的退火处理过程中Cd1-xZnxTe晶体材料电阻率及导电类型变化和扩散杂质的扩散系数之间关系的模型,结合实验数据,获得了1073 K,973 K和873 K下Cd在Cd0.9Zn0.1Te晶体中的扩散系数,并估算了其激活能. 通过使用获得的扩散系数,研究了在不同温度及饱和Cd气氛下,退火时间对Cd0.9Zn0.1Te晶体电阻率分布及导电类型等的变化的影响.