Gettering Properties of Praseodymium in GaAs,In0.53Ga0.47As,and InP Grown by Liquid Phase Epitaxy

The incorporation of praseodymium (Pr) into GaAs, In_0.53Ga_0.47As, and InP during liquid-phase epitaxy were investigated by double crystal x-ray diffraction, Hall effect, low temperature photoluminescence (PL) measurements. The lattice mismatch slightly vary with Pr concentration in the growth melts. Examinations of the electrical property illustrate that the lower carriers concentrations and a higher mobilities are obtain from Pr-doped epilayers than undoped sample (In_0.53Ga_0.47As and InP). The PL spectra (15-K) show that the intensity of the impurity related peaks decreases and the near-band-to-band luminescence intensity increase. They also reveal that the impurities are gettered by Pr ions during LPE growth. Thus, for the purpose of purification, proper amount of Pr in the growth melts is suggested. No intra-4f-shell transition line is observed from the Pr-doped GaAs, In_0.53Ga_0.47As, and InP layers.     

Electro-optical properties of InGaAs layers grown by hydride vapour phase epitaxy

A series of epitaxial layers of the InGaAs alloy were deposited on (001) oriented InP substrates by using hydride VPE technique. The layers were characterized by Double Crystal Diffractometry (DCD), Photoluminescence (PL), Hall effect and Capacitance-Voltage (C-V) measurements. The growth parameters and the quality of the grown layers are discussed on the basis of electrical and structural data analysis.     

Doping Properties of Pr2O3 Associate InP Liquid Phase Epitaxy

InP epilayers were grown on semi-insulating InP substrates by liquid phase epitaxy with Pr₂O₃-doping. Most grown layers yield mirror-like surfaces and good crystal quality. Hall measurements indicate that n-type background concentration of those grown InP layers will decrease from a value of 2.8 × 10¹⁷ to 3.0 × 10¹⁶ cm⁻³. Their correspondent 77 K mobility also varied from a value of 1326 to 3775 cm²/V s. The photoluminescence (PL) spectra of Pr₂O₃-doped InP epilayers display narrower FWHM and stronger intensity ratios (for band peak to the impurity peak). These PL spectra also demonstrate that the grown layers exhibit a pure crystal quality.     

Characterization of InAs quantum dots on lattice-matched InAlGaAs/InP superlattice structures

Self-assembled InAs quantum dots (QDs) in an InAlGaAs matrix, lattice-matched to InP substrate, have been grown by molecular beam epitaxy (MBE). Transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL) are used to study their structural and optical properties. In InAs/InAlGaAs/InP system, we propose that when the thickness of InAs layer deposited is small, the random strain distribution of the matrix layer results in the formation of tadpole-shaped QDs with tails towards random directions, while the QDs begin to turn into dome-shaped and then coalesce to form islands with larger size and lower density to release the increasing misfit strain with the continuous deposition of InAs. XRD rocking curves showing the reduced strain with increasing thickness of InAs layer may also support our notion. The results of PL measurements are in well agreement with that of TEM images.     

Influence of semi-insulating InP substrates on InAlAs epilayers grown by molecular beam epitaxy

Tensile-strained InAlAs layers have been grown by solid-source molecular beam epitaxy on as-grown Fe-doped semi-insulating (SI) InP substrates and undoped SI InP substrates obtained by annealing undoped conductive InP wafers (wafer-annealed InP). The effect of the two substrates on InAlAs epilayers and InAlAs/InP type II heterostructures has been studied by using a variety of characterization techniques. Our calculation data proved that the out-diffusion of Fe atoms in InP substrate may not take place due to their low diffusion coefficient. Double-crystal X-ray diffraction measurements show that the lattice mismatch between the InAlAs layers and the two substrates is different, which is originated from their different Fe concentrations. Furthermore, photoluminescence results indicate that the type II heterostructure grown on the wafer-annealed InP substrate exhibits better optical and interface properties than that grown on the as-grown Fe-doped substrate. We have also given a physically coherent explanation on the basis of these investigations.     

InP/GaP晶格失配界面的电特性

本文研究了InP/GaP晶格失配界面的电特性。HRTEM图象表明在界面存在90°位错缺陷的应变缓释。ECV表明界面存在高密度载流子层。AFM图象表明本研究中获得了粗糙度为2.48nm的良好InP异质外延层。并对于InP界面给出了一个基于费米能级钉扎的模型来解释观察到的电性质。     

固态源MBE系统生长高质量的调制掺杂GaAs结构材料和InP/InP外延材料的兼容性研究

通过固态源的分子束外延系统生长了调制掺杂AlGaAs/GaAs结构材料和InP/InP外延材料.在生长含磷材料之后,生长条件(真空状态)变差;我们通过采取合理的工艺方法和生长工艺条件的优化,获得了电子迁移率为1.86×105cm2/Vs(77K)调制掺杂AlGaAs/GaAs结构材料和电子迁移率为2.09×105cm2/Vs(77K)δ-Si掺杂AlGaAs/GaAs结构材料.InP/InP材料的电子迁移率为4.57×104 cm2/Vs(77K),该数值是目前国际报道最高迁移率值和最低的电子浓度的InP外延材料.成功地实现了在一个固态源分子束外延设备交替生长高质量的调制掺杂AlGaAs/GaAs结构材料和含磷材料.     

Improvements in silicon doping of InP and GaInAs in metalorganic molecular beam epitaxy

We have investigated the Si doping of InP and GaInAs in metalorganic molecular beam epitaxy (MOMBE) by using a conventional Si effusion cell. In order to reduce the formation of SiC promoted by the background gases in MOMBE, we introduced a liquid nitrogen cooled baffle between the cell and the mechanical shutter. The results show that the passivating reaction can be substantially suppressed by a proper treatment of the source cell. The doping efficiency remains constant over a long period of operation corresponding to a large total layer thickness (>100 μm). The comparison of SIMS analysis with Hall data reveals an electrical activation of Si in InP up to 100% and about 65% for Si in GaInAs. These results and the investigations on doping profiles show that Si is a suitable donor in InP and GaInAs in the MOMBE process.     

Influence of growth parameters on the interface abruptness in CBE-grown InGaAs/InP QWs and SLs

A simple thermodynamic model for As and P incorporation at the CBE-grown InGaAs/InP and InP/InGaAs interfaces has been developed. This model agrees with the X-ray diffraction and the photoluminescence features experimentally obtained from high-quality single quantum wells (SQWs) and multi-quantum wells (MQWs). Our experimental results compare well with the best published data and clearly show that monolayer interfaces can be obtained in this material system only by chosing the proper growth interruption (GI) conditions and accepting a strong mismatch at each interface. This effect could become dramatic in superlattice structures in which the QW period is smaller than 5 nm and the resulting strain could lead to poor crystal quality and optical properties.     

Finite element analysis of dislocation density during bulk single crystal growth (effect of doping atoms in InP single crystal)

A computer code for simulation of dislocation density in a bulk single crystal during liquid encapsulated Czochralski (LEC) or Czochralski (CZ) growth process. In this computer code, the shape of crystal–melt interface and the temperature in a crystal at an arbitrary time were determined by linear interpolation of the results that were discretely obtained by heat conduction analysis of a CZ single crystal growth system. A dislocation kinetics model called Haasen–Sumino model was used as a constitutive equation. In this model, creep strain rate is related to dislocation density, and this model extended to multiaxial stress state was incorporated into a finite element elastic creep analysis program for axisymmetric bodies. Dislocation density simulations were performed using this computer code for InP bulk single crystals with about 8″ in diameter. In the analysis, the effect of dopant atoms on the dislocation density was examined. In the case of a low doped InP single crystal, dislocations are distributed in the whole of the crystal. On the other hand, in the case of a highly doped InP single crystal, dislocations are localized at both the central and peripheral regions of the crystal.     

Correlations between photoluminescence and Hall mobility in GaN/sapphire grown by metalorganic chemical vapor deposition

We have investigated photoluminescence (PL) and electron Hall mobility for unintentionally doped GaN epitaxial layers grown by low-pressure metalorganic chemical vapor deposition on c-plane Al₂O₃ substrates. Four GaN films having identical dislocation density but remarkably different electron Hall mobility were exploited. At low temperature (12 K), a PL line associated with a bound exciton was observed and strong correlations were found between the Hall mobility and the PL intensity of the exciton transition. That is, relative PL intensity of the bound exciton to a donor-bound exciton monotonously increased with decreasing the electron mobility of the GaN films. This correlation was interpreted in terms of electrical compensation. Efforts to find the chemical origin of the PL line led to the conclusion that the BE line originated neither from threading dislocations nor from extrinsic point defects. Intrinsic acceptors such as Ga vacancy and GaN anti-site were suspected as plausible origin.     

Role of the substrate deoxidation process in the growth of strained InAs/InP heterostructures

We have investigated the role of the arsenic flux used during the substrate deoxidation process in the MBE (molecular beam epitaxy) growth of strained InAs/InP heterostructures. Two different experiments were performed: (i) thermal cleaning of the InP wafer under an As flux at different exposure times and (ii) the growth of very thin InAs layers (3-9 ML). The samples grown were characterized by Raman spectroscopy and selected area X-ray photoelectron spectroscopy. The results obtained demonstrated the formation of an InAs_xP_1−x sublayer at the interface of the InAs/InP system. The annealing of InP under an As flux promotes not only As → P substitution on the surface, but also the subsequent diffusion of As atoms into the deeper subsurface region of InP.     

p-ZnO薄膜及其异质结的光电性质

采用射频磁控溅射法,在不同的Ar∶O2条件下,以高掺磷n型Si衬底为磷掺杂源制备了p型ZnO薄膜和p-ZnO/n-Si异质结.对ZnO∶P薄膜进行了光致发光谱(PL)、霍尔参数、Ⅰ-Ⅴ特性、扫描电镜(SEM)和X射线衍射谱(XRD)等测试.结果表明,获得的ZnO∶P薄膜沿(0002)晶面高取向生长,以3.33 eV近带边紫外发光为主,伴有2.69 eV附近的深能级绿色发光峰,空穴浓度为8.982 × 1017/cm3,空穴迁移率为9.595 cm2/V·s,p-ZnO/n-Si异质结I-V整流特性明显,表明ZnO∶P薄膜具有p型导电特性.     

Optical properties of self-assembled InAs/InAlAs/InP quantum wires with different InAs deposited thickness

We report on the photoluminescence (PL) properties of InAs/InAlAs/InP quantum wires (QWRs) with various InAs deposited thickness. The PL linewidth of the QWRs decreases with increasing InAs deposited thickness due to the different thicknesses of the QWRs and defects in the samples. The defects and lateral composition modulation of the InAlAs layers play an important role in the temperature-dependent PL properties of the samples.     

Zn-doped AlInAs grown at high temperature by metalorganic chemical vapor deposition

Zn-doped AlInAs growth at high temperature, mainly at 750°C, by metalorganic chemical vapor deposition is investigated. When introducing DEZn during AlInAs growth, it is necessary to increase the TMAl flow rate in order to make the layer lattice-matched to InP. This is due to the enhanced In incorporation rather than the large covalent radius of Zn. To clarify the electrical characteristics, the dependence of the DEZn flow rate, the V/III ratio, and the growth temperature are investigated using the van der Pauw Hall method. In our growth system, a GaInAs intermediate layer is effective in preventing n-type inversion in Zn-doped AlInAs, which occurs when it is grown directly on an InP buffer layer. In addition, a large DEZn flow rate is effective for reducing carrier compensation in Zn-doped AlInAs layers grown at 750°C. Si impurities are apparently the cause of the type-inversion and compensation in Zn-doped AlInAs.     

Large- and selective-area LP-MOVPE growth of InGaAsP-based bulk and QW layers under nitrogen atmosphere

Layer structures comprising InP and InGaAsP were compared when grown using nitrogen versus hydrogen as carrier gas. Under nitrogen a remarkable improvement in layer uniformity in terms of thickness and PL wavelength is obtained for InGaAsP layers over the whole compositional range. This improvement duplicates for the PL wavelength of quantum wells. The selective-area growth behaves differently regarding the excess growth at mesa edges and the wavelength variation in the vicinity of masked areas. The basic laser parameters, especially the threshold current density, of 1.55 μm bulk- and MQW-laser structures show at least equivalent, if not superior data when grown under nitrogen.     

Structural and electrical properties of InAlAs/InGaAs/InAlAs HEMT heterostructures on InP substrates with InAs inserts in quantum well

A complex study of the influence of nanoscale InAs inserts with thicknesses from 1.7 to 3.0 nm introduced into In_0.53Ga_0.47As quantum wells (QWs) on the structural and electrical properties of In_0.52Al_0.48As/In^0.53Ga_0.47As/In_0.52Al_0.48As heterostructures with one-sided δ-Si-doping has been performed. The structural quality of a combined QW was investigated by transmission electron microscopy. A correlation between the electron mobility in QW with the thickness of InAs insert and the technology of its fabrication is established. Specific features of the InP(substrate)/InAlAs(buffer) interface are investigated by transmission electron microscopy and photoluminescence spectroscopy. A relationship between the energy positions of the peak in the photoluminescence spectra in the range of photon energies 1.24 eV < ?ω < 1.38 eV, which is due to the electronic transitions at the InP/InAlAs interface, and the structural features revealed in the interface region is established. It is found that an additional QW is unintentionally formed at the InP/InAlAs interface; the parameters of this QW depend on the heterostructure growth technology.     

Growth of InP in chemical beam epitaxy with high purity tertiarybutylphosphine

InP layers were grown by chemical beam epitaxy (CBE) using high purity thermally precracked tertiarybutylphosphine (TBP) and trimethylindium (TMI) as the source of the group III element. For optimized substrate temperature and V/III ratio, InP films of good electrical and optical quality have been obtained; the n-type background carrier concentration is (1–2) × 10¹⁵ cm^-3, with a Hall mobility at 77 K being μ₇₇ = 45,000 cm² V^-1 s^-1. Given the low value of the V/III ratio, and according to mass spectrosc measurements, the phosphorus species giving rise to epitaxy is expected to be the dimer P₂. The TBP consumption in CBE is very low when compared to organometallic vapour phase epitaxy (OMVPE), typicaly below 0.25 g/μm of InP layer.     

Modeling analysis of liquid encapsulated Czochralski growth of GaAs and InP crystals

The results of three‐dimensional unsteady modeling of melt turbulent convection with prediction of the crystallization front geometry in liquid encapsulated Czochralski growth of InP bulk crystals and vapor pressure controlled Czochralski growth of GaAs bulk crystals are presented. The three‐dimensional model is combined with axisymmetric calculations of heat and mass transfer in the entire furnace. A comprehensive numerical analysis using various two‐dimensional steady and three‐dimensional unsteady models is also performed to explore their possibilities in predicting the melt/crystal interface geometry. The results obtained with different numerical approaches are analyzed and compared with available experimental data. It has been found that three‐dimensional unsteady consideration of heat and mass transfer in the crystallization zone provides a good reproduction of the solidification front geometry for both GaAs and InP crystal growth.     

A Study of Convection,Striations and Interface Shape in InP Crystals Grown by the Double-Crucible LEC Technique

A doublecrucible (DC) Czochralski setup has been used for the pulling of semi-insulating Fe-doped InP. The level of the Fe-doped melt in the growth crucible is replanished with the undoped InP from the reservoir crucible. In this way, since the distribution coefficient of iron is very small (about 0.001), the Fe concentration in the growth crucible is virtually unchanged during the pulling so that the axial Fe concentration is much more uniform than in standard LEC crystals. The use of two concentric crucibles has great implications in terms of convective flows, stability of the melt temperature and interface shape. In this paper we report the results of a study on striations and structural defects in InP grown from a double-crucible LEC arrangement. A dimensionless relationship for correlating striation features with melt motions is also proposed.