GaSb layers with low defect density deposited on (001) GaAs substrate in two-dimensional growth mode using molecular beam epitaxy

We report on the growth of fully relaxed and smooth GaSb layers with reduced density of threading dislocations, deposited on GaAs substrate. We prove that three parameters have to be controlled in order to obtain applicable GaSb buffers with atomically smooth surface: interfacial misfit (IMF), the etch pit density (EPD) and the growth mode.The GaSb/GaAs interfacial misfit array and reduced EPD ≤1.0 × 10⁷ cm^?2 were easily obtained using As-flux reduction for 3 min and Sb-soaking surface for 10 s before the GaSb growth initiation. The successive growth of GaSb layer proceeded under the technological conditions described by the wide range of the following parameters: r_G ∈ (1.5 ÷ 1.9) Å/s, T_G ∈ (400 ÷ 520)°C, V/III ∈ (2.3 ÷ 3.5). Unfortunately, a spiral or 3D growth modes were observed for this material resulting in the surface roughness of 1.1 ÷ 3.0 nm. Two-dimensional growth mode (layer by layer) can only be achieved under the strictly defined conditions. In our case, the best quality 1-μm-thick GaSb buffer layer with atomically smooth surface was obtained for the following set of parameters: r_G = 1.5 Å/s, T_G = 530 °C, V/III = 2.9. The layer was characterized by the strain relaxation over 99.6%, 90° dislocations array with the average distance of 5.56 nm, EPD ～8.0 × 10⁶ cm^?2 and 2D undulated terraces on the surface with roughness of about 1 ML. No mounds were observed. We belive that only thin and smooth GaSb layer with reduced EPD may be applied as the buffer layer in complex device heterostructures. Otherwise, it may cause the device parameters deterioration.     

Combined RHEED-AES study of the thermal treatment of (001) GaAs surface prior to MBE growth

Auger analysis and reflection high energy electron diffraction (RHEED) have been used to study the UHV thermal cleaning procedure of different chemically treated (001) GaAs surfaces when heated in ultra high vacuum. It is shown that the ultimate surface composition of the substrate critically depends on the nature and the thickness of the oxide layer formed during chemical treatment. The oxygen removal mechanism has been studied and a comparative analysis of AES and RHEED observations has been drawn. A low residual carbon coverage cleaning procedure is fully investigated and it results that a carbon coverage as low as ∼6×10⁻² monolayer induces surface faceting by heating the GaAs substrate at temperatures higher than 570°C. A (001) GaAs surface heated in an arsenic flux up to 570°C is As-stabilized and (411) facets appear at a temperature ranged between 575 and 585°C.     

Leed,aes and photoemission measurements of epitaxially grown GaAs(001), (111)A and (1̄1̄1̄)B surfaces and their behaviour upon cs adsorption

Epitaxially grown GaAs(001), (111) and (1?1?1?) surfaces and their behaviour on Cs adsorption are studied by LEED, AES and photoemission. Upon heat treatment the clean GaAs(001) surface shows all the structures of the As-stabilized to the Ga-stabilized surface. By careful annealing it is also possible to obtain the As-stabilized surface from the Ga-stabilized surface, which must be due to the diffusion of As from the bulk to the surface. The As-stabilized surface can be recovered from the Ga-stabilized surface by treating the surface at 400°C in an AsH₃ atmosphere. The Cs coverage of all these surfaces is linear with the dosage and shows a sharp breakpoint at 5.3 × 10¹⁴ atoms cm^?2. The photoemission reaches a maximum precisely at the dosage of this break point for the GaAs(001) and GaAs(1?1?1?) surface, whereas for the GaAs(111) surface the maximum in the photoemission is reached at a higher dosage of 6.5 × 10¹⁴ atoms cm^?2. The maximum photoemission from all surfaces is in the order of 50μA Im^?1 for white light (T = 2850 K). LEED measurements show that Cs adsorbs as an amorphous layer on these surfaces at room temperature. Heat treatment of the Cs-activated GaAs (001) surface shows a stability region of 4.7 × 10¹⁴ atoms cm^?2 at 260dgC and one of 2.7 × 10¹⁴ atoms cm^?2 at 340°C without any ordering of the Cs atoms. Heat treatment of the Cs-activated GaAs(111) crystal shows a gradual desorption of Cs up to a coverage of 1 × 10¹⁴ atoms cm^?2, which is stable at 360°C and where LEED shows the formation of the GaAs(111) (√7 × √7)Cs structure. Heat treatment of the Cs-activated GaAs(1?1?1?) crystal shows a stability region at 260°C with a coverage of 3.8 × 10¹⁴ atoms cm^?2 with ordering of the Cs atoms in a GaAs(1?1?1?) (4 × 4)Cs structure and at 340°C a further stability region with a coverage of 1 × 10¹⁴ at cm^?2 with the formation of a GaAs(1?1?1?) (√21 × √21)Cs structure. Possible models of the GaAs(1?1?1?) (4 × 4)Cs, GaAs(1?1?1?)(√21 × √21)Cs and GaAs(111) (√7 × √7)Cs structures are given.     

Effects of V/III ratio on the growth of a-plane GaN films

The non-polar a-plane GaN is grown on an r-plane sapphire substrate directly without a buffer layer by metal-organic chemical vapour deposition and the effects of V/III ratio growth conditions are investigated. Atomic force microscopy results show that triangular pits are formed at a relatively high V/III ratio, while a relatively low V/III ratio can enhance the lateral growth rate along the c-axis direction. The higher V/III ratio leads to a high density of pits in comparison with the lower V/III ratio. The surface morphology is improved greatly by using a low V/III ratio of 500 and the roughness mean square of the surface is only 3.9 nm. The high resolution X-ray diffraction characterized crystal structural results show that the rocking curve full width at half maximum along the m axis decreases from 0.757° to 0.720°, while along the c axis increases from 0.220° to 0.251° with the V/III increasing from 500 μmol/min to 2000 μmol/min, which indicates that a relatively low V/III ratio is conducible to the c-axis growth of a-plane GaN.     

The evaporation of GaAs under equilibrium and non-equilibrium conditions using a modulated beam technique

The evaporation of GaAs under both Knudsen and Langmuir conditions has been studied using a quadrupole resonance mass spectrometer. Particular care was taken to separate beam from background signals by modulating the evaporation fluxes using a mechanical chopper. In the temperature range 850–1100°K, the arsenic vapour flux from GaAs consists mainly of As₂ under both Knudsen and Langmuir conditions. Vapour pressure data for gallium and arsenic over GaAs are presented. A congruent evaporation point occurs at 898°K under Knudsen conditions. Under Langmuir conditions, GaAs evaporates congruently below 930°K but above this temperature arsenic is lost preferentially. Under Langmuir conditions constant evaporation rates were not observed from a {100} surface at any temperature studied.     

The initial growth of Au on GaAs(001)-c(4 × 4)

The metal growth when depositing a monolayer (ML) of Au at 200° C on MBE-grown surfaces of GaAs(001)-c(4 × 4) was studied by AES and RHEED. The surface interaction can be characterized to proceed in two stages depending on the surface coverage of Au. At a coverage of less than 0.3 ML the gold atoms are mainly dispersed on the surface with a small in depth diffusion. Above 0.4 ML there is a rapid intermixing and a tendency of arsenic accumulation to the surface.     

Transmutation doping of GaAs by thermal neutrons

The electrical properties of GaAs have been modified by transmutation of about 1 × 10¹⁸ As atoms per cm³ to Se and 0.7 × 10¹⁸ Ga atoms per cm³ to Ge in a flux of thermal neutrons, followed by annealing at temperatures from 625 to 900°C. Enhancement of carrier concentration was not observed in n⁺ samples, although p and n^? material showed changes in carrier concentration of the expected magnitude.     

Surfactant properties of cesium in molecular beam epitaxy of GaAs(100)

The experimental and ab initio investigations of the effect of a decrease in the binding energy of surface arsenic atoms under the cesium adsorption on an As-stabilized GaAs(001)-(2 × 4) surface have been performed. The cesium-induced redistribution of the charge on the surface atoms reduces the electron density in the As-Ga bond of the upper layer of the GaAs(001) surface; thus, the As-Ga binding energy decreases and, as a result, the diffusion activation energy, as well as the arsenic atom desorption, decreases. An increase in the diffusion coefficient of surface atoms, along with the property of Cs to segregate on the surface of a growing semiconductor film, makes it possible to use cesium as a surfactant in the low-temperature growth of GaAs by molecular beam epitaxy.     

Lattice location and thermal annealing behaviour studies of GaAs single crystals implanted with Co-atoms

Co-atoms have been implanted into n-type GaAs single crystals up to a dose of 2×10¹⁵ atoms/cm². Mössbauer Spectroscopy was used together with Proton Induced X-ray Excitation and Rutherford Backscattering Spectrometry in Channeling geometry to study the recovery of the GaAs-crystal from the implantation damage and the final lattice locations of the Co-atoms. Epitaxial regrowth of the GaAs was found to take place in the annealing temperature region from 300°–450°C. At 900°C rapid thermal annealing an epitaxial Co-phase was found at the surface with the Co-atoms partially blocking the GaAs <110> channel.     

GaSb/GaAs复合应力缓冲层上自组装InAs量子点的生长

研究了GaSb/GaAs复合应力缓冲层上自组装生长的InAs量子点.在2ML GaSb/1ML GaAs复合应力缓冲层上获得了高密度的、沿［100］方向择优分布量子点.随着复合应力缓冲层中GaAs层厚度的不同,量子点的密度可以在1.2×10¹⁰cm^-2和8×10¹⁰cm^-2进行调控.适当增加GaAs层的厚度至5ML,量子点的发光波长红移了约25nm,室温下PL光谱波长接近1300nm. 关键词： 自组装量子点 分子束外延 Ⅲ-Ⅴ族化合物半导体     

Decrease in the bond energy of arsenic atoms on the GaAs(100)-(2×4)/c(2×8) surface due to the effect of adsorbed cesium

It has been found experimentally that the bond energy of arsenic atoms on the GaAs(100) surface decreases under the influence of adsorbed cesium. This is manifested in the disordering of the As-stabilized surface and in a decrease of ～(100 K in the temperature of the transition to the Ga-stabilized (100)GaAs(4×2)/c(8×2) surface. This effect is caused by the redistribution of the valence electron density between the arsenic atoms in the upper layer and the gallium atoms in the lower-lying layer as a result of charge transfer from the electropositive adsorbate to the semiconductor. In combination with the analogous effect of a decrease in the bonding energy of gallium atoms on the Ga-stabilized GaAs surface upon the adsorption of electronegative adsorbates (halogens), the effect observed allows the atomic layer etching of the polar GaAs(100) face.     

Investigation of X-ray diffraction limitations upon the analysis of tellurium-atom injection into GaAs epitaxial layers

GaAs lattice “superdilation” caused by an introduced tellurium impurity, which is well known in publications, is experimentally studied. This phenomenon consists in the fact that the GaAs-lattice dilation can be more than 10 times greater than expansion that would appear upon the replacement of arsenic atoms with tellurium atoms if calculations are performed using the current-carrier concentration and Vegard’s law. The given phenomenon has already been observed at n _Te > 3 × 10¹⁸ cm^–3. A series of GaAs epitaxial layers heavily doped with tellurium and grown via metal-organic chemical vapor deposition are investigated using high-resolution X-ray diffractometry (HRXRD), secondary-ion mass spectrometry (SIMS), and the Hall effect. It is demonstrated that, despite a high Te concentration (10²⁰?10²¹ cm^–3) in the layer and variations in the growth conditions, the concentration estimates based on HRXRD data depend linearly on the results of elemental analysis performed by means of SIMS. The GaAs lattice expands even somewhat slighter as compared to the case where arsenic atoms are replaced with all Te atoms injected into the layer. At the same time, the Hall carrier concentration decreases sharply beginning at 2 × 10²⁰ cm^–3. In accordance with the obtained results, the examined phenomenon can be interpreted as the strong compensation of donor and acceptor carriers rather than as superdilation.     

Effects of MBE growth conditions on carbon contamination in GaAs

The effects of growth and pre-growth conditions on the background concentration of carbon in high quality undoped GaAs layers grown by molecular beam epitaxy have been studied. Characterization of the layers by low temperature photoluminescence indicates that a growth temperature of 580°C minimizes carbon contamination, and extended pre-growth outgassing of the substrate under an As₄ over-pressure results in increased carbon concentrations. The carbon incorporation was found to be relatively insensitive to outgassing temperature above 615°C. Contrary to expectations, increasing the As/Ga flux ratio during growth resulted in larger carbon luminescence peaks.     

Self-assembled InAs island formation on GaAs (1 1 0) by metalorganic vapor phase epitaxy

Formation of self-assembled InAs 3D islands on GaAs (1 1 0) substrate by metal organic vapor phase epitaxy has been investigated. Relatively uniform InAs islands with an average areal density of 10⁹ cm⁻²are formed at 400 ° C using a thin InGaAs strain reducing (SR) layer. No island formation is observed without the SR layer. Island growth on GaAs (1 1 0) is found to require a significantly lower growth temperature compared to the more conventional growth on GaAs (1 0 0) substrates. In addition, the island height is observed to depend only weakly on the growth temperature and to be almost independent of the V/III ratio and growth rate. Low-temperature photoluminescence at 1.22 eV is obtained from the overgrown islands.     

Suppressed intermixing in InAlGaAs/ AlGaAs/GaAs and AlGaAs/GaAs quantum well heterostructures irradiated with a KrF excimer laser

The influence of gallium arsenide surface modification induced by irradiation with a KrF excimer laser on the magnitude of the quantum well (QW) intermixing effect has been investigated in InAlGaAs/AlGaAs/GaAs QW heterostructures. The irradiation in an air environment with laser pulses of fluences between 60 and 100 mJ/cm² has resulted in the formation of a gallium oxide-rich film at the surface. Following the annealing at 900 °C, up to 35 nm suppression of the band gap blue shift was observed in all the laser irradiated samples when compared to the non-irradiated samples. The origin of suppression has been discussed in terms of stress controlled diffusion. PACS 78.55.Et; 66.30.Lw; 73.21.Fg     

Growth and characterization of DyP/GaAs and DyAs/GaAs-based heterostructures and superlattices

Details of the structural and electrical properties of epitaxial DyP/GaAs and DyAs/GaAs is reported. DyP is lattice matched to GaAs, with a room temperature mismatch of less than 0.01%. DyAs, on the other hand, has a mismatch of nearly 2.4%. Both DyP and DyAs have been grown by solid source MBE using custom designed group V thermal cracker cells and group III high-temperature effusion cells. High-quality DyP and DyAs epilayers, as determined by XRD, TEM, and AFM analysis, were obtained for growth temperatures ranging from 500°C to 600°C with growth rates between 0.5 and 0.7 μm/h. The DyP epilayers are n-type with measured electron concentrations of the order of 3×10²⁰ to 4×10²⁰ cm⁻³, with room temperature mobilities of 250–300 cm²/V s, and with a barrier height of 0.75 eV to GaAs. The DyAs epilayers are also n-type with concentration of 1×10²¹ to 2×10²¹ cm⁻³, with mobilities between 25 and 40 cm²/V s. DyP is stable in air with no apparent oxidation taking place, even after months of ambient exposure to untreated air.     

Divacancy complexes induced by Cu diffusion in Zn-doped GaAs

Positron annihilation spectroscopy was applied to investigate the nature and thermal behavior of defects induced by Cu diffusion in Zn-doped p-type GaAs crystals. Cu atoms were intentionally introduced in the GaAs lattice through thermally activated diffusion from a thin Cu capping layer at 1100 °C under defined arsenic vapor pressure. During isochronal annealing of the obtained Cu-diffused GaAs in the temperature range of 450?850 K, vacancy clusters were found to form, grow and finally disappear. We found that annealing at 650 K triggers the formation of divacancies, whereas further increasing in the annealing temperature up to 750 K leads to the formation of divacancy-copper complexes. The observations suggest that the formation of these vacancy-like defects in GaAs is related to the out-diffusion of Cu. Two kinds of acceptors are detected with a concentration of about 10¹⁶ ? 10¹⁷ cm^?3, negative ions and arsenic vacancy copper complexes. Transmission electron microscopy showed the presence of voids and Cu precipitates which are not observed by positron measurements. The positron binding energy to shallow traps is estimated using the positron trapping model. Coincidence Doppler broadening spectroscopy showed the presence of Cu in the immediate vicinity of the detected vacancies. Theoretical calculations suggested that the detected defect is V _Ga V _As-2Cu_Ga.     

Lattice site location and electronic structure of Te in GaAs

High purity <100> wafers of GaAs were implanted with radioactive^129mTe and stable¹²⁸Te at 110 keV to total doses of 2×10¹⁴ and 2×10¹⁵ Te/cm² respectively and studied with RBS/ channeling and Mössbauer spectroscopy on the 27.8 keV level of¹²⁹I. After implantation and/or annealing at temperatures between 200–300°C the Mössbauer spectra are dominated by a single line. Channeling reveals an appreciable residual damage in the host lattice, but also points to a substitutional position of the Te atoms. After annealing above ≌500°C, where nearly complete lattice damage recovery is obtained, the Te atoms become defect-associated. The results clearly point to the formation of Te_As?V_Ga complexes.     

关于RHEED振荡技术优化GaAs(110)量子阱生长的研究

在GaAs(110)衬底上生长的半导体材料有诸多优良性能，使得在非极性GaAs(110)衬底上获得高质量各类异质结材料，成为近年来分子束外延生长关注的课题.考虑GaAs(110)表面是Ga和As共面，最佳生长温度窗口很小；反射式高能电子衍射的(1×1)再构图案对生长温度和V/Ⅲ束流比不敏感，难于通过观察再构图案的变化，准确地找到最佳生长条件.作者在制备GaAs(110)量子阱过程中，观察到反射式高能电子衍射强度振荡呈现出的单双周期变化.这意味着不同工艺条件下，在 GaAs(110)衬底上量子阱有单层和双层两种生长模式.透射电子显微镜和室温光致荧光光谱测量结果表明：在双层生长模式下量子阱样品光学性能较差，而在单层生长模式下量子阱光学性能较好，但是界面会变粗糙.利用这一特点，我们采用反射式高能电子衍射强度振荡技术，找到了一种在GaAs(110)衬底上生长高质量量子阱的可行方法. 关键词： 反射高能电子衍射 量子阱 分子束外延     

Characteristics of Germanium n+/p junctions formed by phosphorus diffusion from on indium-gallium-phosphide layer

Although numerous studies have been previously reported for the formation of Ge p–n junctions, there is still a lack of research on Ge junctions formed by solid-phase diffusion doping, which typically uses the diffusion phenomenon of phosphorus (P) atoms from InGaP for the fabrication of a Ge n⁺/p subcell in a III–V multi-junction cell. Here, we investigate the characteristics of Ge n⁺/p junctions achieved by the InGaP-based diffusion technique at 450–650 °C with SIMS, ECV, and J–V analyses. In addition, through a multiple error function fitting method, diffusivity, peak position, and activation energy values are accurately estimated from raw In/Ga/P/Ge SIMS profiles. The extracted activation energy values for In/Ga/P atoms are much lower than previously reported, indicating that a faster diffusion phenomenon occurs during the simultaneous diffusion of In/Ga/P into Ge. A non-annealed InGaP-deposited junction shows Ohmic behavior with a high current density because of leakage currents by many interfacial point defects. After a 550 °C anneal, the current density is reduced by 3–4 orders of magnitude and a small on/off-current ratio is obtained. Compared to this 550 °C annealed junction, a current density increases ∼10 times in the 650 °C sample due to an increased n-type carrier concentration.