Se-doped AlGaAs grown on GaAs(111)A by molecular beam epitaxy

The electrical properties of Se-doped Al_0.3Ga_0.7As layers grown by molecular beam epitaxy (MBE) on GaAs(111)A substrates have been investigated by Hall-effect and deep level transient spectroscopy (DLTS) measurements. In Se-doped GaAs layers, the carrier concentration depends on the misorientation angle of the substrates; it decreases drastically on the exact (111)A surface due to the re-evaporation of Se atoms. By contrast, in Se-doped AlGaAs layers, the decrease is not observed even on exact oriented (111)A. This is caused by the suppression of the re-evaporation of Se atoms, by Se---Al bonds formed during the Se-doped AlGaAs growth. An AlGaAs/GaAs high electron mobility transistor (HEMT) structure has been grown. The Hall mobility of the sample on a (111)A 5° off substrate is 5.9×10⁴ cm²/V·s at 77 K. This result shows that using Se as the n-type dopant is effective in fabricating devices on GaAs(111)A.     

Diffusion of Si-acceptor in δ-doped GaAs grown on GaAs(111)A by molecular beam epitaxy

Diffusion of Si-acceptors (Si occupying As sites) in δ-doped GaAs grown on GaAs(111)A has been investigated by secondary ion mass spectrometry (SIMS). We have measured the diffusion parameters in GaAs(111)A and found that they differ from those in GaAs(001). The diffusion coefficient in GaAs(111)A is smaller than that in GaAs(001) and the activation energy in GaAs(111)A is larger than that in GaAs(001). Furthermore, the diffusion mechanism of Si in GaAs(111)A has been investigated by photoluminescence; we have found that in p-type layers Si-donors (Si occupying Ga sites) diffuse easily to As sites. The activation energy of Si-acceptor diffusion is 2.74±0.11 eV. These results indicate that Si-acceptors are more stable than Si-donors.     

Reflection high-energy electron diffraction intensity oscillations during growth of (Al,Ga)As on GaAs(111)A

We have made a reflection high-energy diffraction (RHEED) intensity oscillation study of the growth of (Al,Ga)As on GaAs and (Al,Ga)As (111)A surfaces. The RHEED intensity oscillations during growth of (Al,Ga)As are dependent on both growth temperature and As₄:Ga flux ratio. In addition, the oscillation period decreases as the Al fraction in the (Al,Ga)As is increased. Changes in the oscillation period during growth of the first few monolayers of both GaAs on (Al,Ga)As and (Al,Ga)As on GaAs may indicate the intermixing of Al and Ga near the heterointerface.     

Aspects of low heterostructure symmetry in (311)A (In,Ga)As/GaAs

We investigate the structural and optical properties of (In,Ga)As/GaAs heterostructures induced by the low symmetry of the [311]A orientation. High-resolution X-ray diffraction (HRDXD) measurements reveal the existence of a shear-strained unit cell. The onset of relaxation in heavily strained structures leads to pronounced anisotropies and to satellite splittings in the X-ray diffraction patterns. Optical investigations indicate that the impact of the piezoelectric fields on the ground state energy is compensated for by In segregation. Nevertheless these fields cause a pronounced reduction of the excitonic binding energy in the (311)A structures.     

Tin as an n-type dopant in the molecular beam epitaxial growth of GaAs(111)A

We have made a systematic study of the tin doping of GaAs layers grown on GaAs(111)A substrates using molecular beam epitaxy (MBE). A series of samples were grown with a range of substrate temperatures (from 460 to 620°C), As:Ga flux ratios (5:1 to 25:1) and tin concentrations (10¹⁶ to 10²⁰ atoms cm⁻³). Layers grown on (111)A surfaces were n-type (in contrast to silicon doping) but with carrier concentrations dependent on growth conditions. We have used secondary ion mass spectrometry (SIMS) measurements to confirm the concentration of tin incorporated and its distribution within the layers.     

Effect of substrate orientation on growth rate and doping level of vapour grown GaAs. Interval (111)A—(100)—(111)B

The effect of the substrate orientation and the supersaturation on the growth rate and doping level of vapor grown GaAs is considered. Experimental results are discussed in terms of crystal growth theory developed by BURTON , CABRERA , FRANK and CHERNOV (BCFCh). It is shown that the main predictions of theory are in agreement with the experimental results. At the same time experimental results, on the whole, are more complicated than predicted by simple crystal growth model. It can be concluded that the BCFCh-theory is applicable for analysing the growth rate and doping level anisotropy for vapor grown crystals.     

The growth and physics of ultra-high-mobility two-dimensional hole gas on (311)A GaAs surface

We report on the molecular beam epitaxy growth of modulation-doped GaAs-(Ga,Al)As heterostructures on the (311)A GaAs surface using silicon as the acceptor. Two-dimensional hole gases (2DHGs) with low-temperature hole mobility exceeding 1.2×10⁶ cm² V⁻¹ s⁻¹ with carrier concentrations as low as 0.8×10¹¹ cm⁻² have been obtained. This hole mobility is the highest ever observed at such low densities by any growth technique. We also report the first observation of persistent photoconductivity in a 2DHG. An analysis of the number density and temperature dependence of the mobility leads us to conclude that the mobility is limited by phonon scattering above 4 K and interface scattering at lower temperatures.     

Molecular beam epitaxy (MBE) growth and structural properties of GaN and AlN on 3C-SiC(0 0 1) substrates

AlN and GaN was deposited by molecular beam epitaxy (MBE) on 3C-SiC(0 0 1) substrates on low-temperature (LT) GaN and AlN buffer layers. It is shown that not only GaN but also epitaxial AlN can be stabilized in the metastable zincblende phase. The zincblende AlN is only obtained on a zincblende LT-GaN buffer layer; on the other hand, AlN crystallizes in the wurtzite phase if it is grown directly on a 3C-SiC(0 0 1) substrate or on a LT-AlN buffer layer. The structural properties of the layers and in particular the orientation relationship of the wurtzite AlN on the 3C-SiC(0 0 1) were analyzed by conventional and high-resolution transmission electron microscopy.     

X-ray Diffraction Analysis of the Structure In0.53Ga0.47As Films Grown on (100) and (111)A GaAs Substrates with a Metamorphic Buffer

Crystallography Reports - Epitaxial In0.53Ga0.47As films, grown on GaAs substrates with the (100) and (111)А crystallographic orientations in the standard high-temperature and low-temperature...     

Controllable cubic and hexagonal GaN growth on GaAs(0 0 1) substrates by molecular beam epitaxy

Two kinds of GaN samples were grown on GaAs(0 0 1) substrates. One is grown on nitridized GaAs surface, the other is grown on nitridized AlAs buffer GaAs substrate. X-ray diffraction and photoluminescence measurements find that the GaN sample directly grown on GaAs substrate is pure cubic phase and those grown on AlAs buffer is pure hexagonal phase. The present study shows that the phase of GaN samples grown on GaAs substrates can be controlled using different buffer layers.     

(Ga, Gd, As) film growth on GaAs substrate by low-energy ion-beam deposit

(Ga, Gd, As) film was fabricated by the mass-analyzed dual ion-beam epitaxy system with the energy of 1000 eV at room temperature. There was no new peak found except GaAs substrate peaks (0 0 2) and (0 0 4) by X-ray diffraction. Rocking curves were measured for symmetric (0 0 4) reflections to further yield the lattice mismatch information by employing double-crystal X-ray diffraction. The element distributions vary so much due to the ion dose difference from AES depth profiles. The sample surface morphology indicates oxidizing layer roughness is also relative to the Gd ion dose, which leads to islandlike feature appearing on the high-dose sample. One sample shows ferromagnetic behavior at room temperature.     

Extremely flat interfaces in GaAs/AlGaAs quantum wells with high Al content(0.7) grown on GaAs (411)A substrates by molecular beam epitaxy

Effectively atomically flat interfaces over a macroscopic area (200 μm diameter) have been achieved in GaAs/Al_0.7Ga_0.3As quantum wells (QWs) with well widths of 3.6-12 nm grown on (411)A GaAs substrates by molecular beam epitaxy (MBE) for the first time. A single and very narrow photoluminescence peak (FWHM, full width at half maximum, is 6.1 meV) was observed at 717.4 nm for the QW with a well width of 3.6 nm at 4.2 K. The linewidth is comparable to that of growth-interrupted QWs grown on (100)-oriented GaAs substrates by MBE. A 1.5 μm thick Al_0.7Ga_0.3As layer with good surface morphology also could be grown on (411)A GaAs substrates in the entire growth temperature region of 580-700°C, while rough surfaces were observed in Al_0.7Ga_0.3As layers simultaneously grown on (100) GaAs substrates at 640-700°C. These results indicate that the surface of GaAs and Al_0.7Ga_0.3As grown on the (411)A GaAs substrates are extremely flat and stable on the (411)A plane.     

Realization of optically active strained InAs island quantum boxes on GaAs(100) via molecular beam epitaxy and the role of island induced strain fields

We report here the realization of strained InAs three-dimensional islands on GaAs(100) with optical characteristics that reveal lateral quantum confinement (i.e. quantum box behavior). The importance of the cap layer growth conditions and methodology in achieving optically active InAs islands and the existence, range, and impact of island-induced strain fields on the cap layer growth are uncovered via marker layer experiments. Strong optical emission from the InAs islands is observed in correlation with the transmission electron microscope (TEM) observation of uniform coherent islands under optimized growth conditions. Photoluminescence excitation (PLE) spectroscopy reveals the presence of the energy transitions due to the three-dimensional electronic confinement in such InAs islands. The InAs islands buried under the GaAs were found to be quite stable upon annealing to 100°C higher than the growth temperature.     

Preferential migration of indium atoms on the (411)A plane in InGaAs grown on GaAs channeled substrates by molecular beam epitaxy

Lateral profiles of In content in a 1.5 μm thick In_xGa_1−xAs (x 0.2) layer grown on GaAs channeled substrates (CSs) with (411)A side-slopes by molecular beam epitaxy (MBE) have been investigated with the use of energy dispersive X-ray spectroscopy (EDX). The observed profiles of the In content suggested that In atoms migrate preferentially in the [1 ] direction on the (411)A plane during MBE growth. This preferential migration of In atoms along [1 ] on the (411)A plane was confirmed by comparing observed lateral profiles of In content in InGaAs layers grown on GaAs CSs and simulated In profiles which are calculated by taking into account of an additional one-way flow of In atoms along [1 ].     

Growth of embedded ErAs nanorods on (4 1 1)A and (4 1 1)B GaAs by molecular beam epitaxy

The low solubility of Er in GaAs results in the formation of ErAs nanostructures when GaAs is grown with 5–6 at% Er/Ga ratio by molecular beam epitaxy on GaAs surfaces. For growth on the (4 1 1)A GaAs surface, cross-sectional scanning transmission electron microscopy images show the presence of ErAs nanorods embedded in a GaAs matrix extending along the [2 1 1] direction with a spacing of roughly 7 nm and a diameter of roughly 2 nm. Growth on the GaAs (4 1 1)B surface resulted in only nanoparticle formation. Variation of the polarized optical absorption with in-plane polarization angle is consistent with coupling to surface plasmon resonances of the semimetallic nanostructures.     

Transmission electron microscopy observation of GaAs/Al0.3Ga0.7As T-shaped quantum well structure fabricated by glancing angle molecular beam epitaxy on GaAs(100) reverse-mesa etched substrates

GaAs/Al_0.3Ga_0.7As multi-layer structures were grown on GaAs (100) reverse-mesa etched substrates by glancing angle molecular beam epitaxy (GA-MBE). A(111)B facet was formed as a side-facet. Surface migration of Ga and Al atoms from the (100) flat region to the (111)B side-facet region has been investigated to fabricate T-shaped GaAs/AlGaAs quantum wells (QWs) under the condition that Ga and Al atoms impinge only an the (100) flat region and do not impinge on the (111)B side-facet. Observation of T-shaped GaAs/AlGaAs quantum wires (QWRs) by cross-sectional transmission electron microscopy (TEM) revealed that there is no migration of Al atoms from the (100) to the (111)B facet region at a substrate temperature (T_s) as high as 630°C, under a V/III ratio of 28 (in pressure ratio). On the other hand, very thin GaAs epitaxial layers grown on the (111)B side-facet region owing to the Ga migration were observed for substrate temperatures of 600 and 630°C. It was found that the mass flow of Ga atoms from the (100) region to the (111)B side-facet region increases, with the thermal activation energy of 2.0 eV, as the substrate temperature increases from 570 to 630°C. The GA-MBE growth on a reverse-mesa etched GaAs substrate at a low temperature 570°C or lower is desirable to fabricate a nm-scale GaAs/AlGaAs QWR structure with nm-scale precision.     

Simultaneous reflection high-energy electron diffraction oscillations and mass spectroscopy investigations during molecular beam epitaxy growth of (001) GaAs - smooth surfaces or stoichiometric films?

Film composition and surface morphology of molecular beam epitaxy (MBE)-grown GaAs(001) surfaces were investigated in situ as a function of flux ratio J_Ga/J_As4. The flux of As₄ molecules desorbing from the sample surface was measured with a quadrupole mass spectrometer (QMS) simultaneously with the observation of reflection high energy electron diffraction (RHEED) intensity oscillations. The incorporation ratio, given by the number of incorporated Ga atoms per As atom, was calculated independent of both the QMS data and the decreasing growth rate for growth conditions with As deficiency, as obtained from the RHEED oscillation frequency. Stoichiometric growth was found up to a flux ratio J_Ga/J_As4 ≈ 0.9. At flux ratios of 1.1 to 1.2, a minimum of the damping of the RHEED oscillation amplitude indicates a very smooth growth front profile, but Ga excess appears to be incorporated mainly in As sites without disturbing the crystal lattice. This assumption was confirmed by photoluminescence (PL) spectroscopy of films grown at a flux ratio J_Ga/J_As4 of 1.2. An additional PL peak was observed, which indicates the incorporation of Ga atoms on As sites.     

Epitaxial low-temperature growth of In<Subscript>0.5</Subscript>Ga<Subscript>0.5</Subscript>As films on GaAs(100) and GaAs(111)<Emphasis Type="Italic">A</Emphasis> substrates using a metamorphic buffer

A complex investigation of epitaxial In_0.5Ga_0.5As films grown on GaAs substrates with crystallographic orientations of (100) and (111)A in the standard high- and low-temperature modes has been performed. The parameters of the GaAs substrate and In_0.5Ga_0.5As film were matched using the technology of step-graded metamorphic buffer. The electrical and structural characteristics of the grown samples have been studied by the van der Pauw method, atomic force microscopy, scanning electron microscopy, and transmission/ scanning electron microscopy. The surface morphology is found to correlate with the sample growth temperature and doping with silicon. It is revealed that doping of low-temperature In_0.5Ga_0.5As layers with silicon significantly reduces both the surface roughness and highly improves the structural quality. Pores 50–100 nm in size are found in the low-temperature samples.     

Influence of initial growth parameters on the structural and optical properties of GaAs on (001) Si

The structural and optical properties of GaAs on (001) Si substrates were investigated by transmission electron microscopy (TEM) and low-temperature photoluminescence (PL). It was found that the success of the two-step growth technique is controlled by the quality (morphology and defect density) of the low-temperature grown AlGaAs nucleation layer. GaAs epilayers grown on low V/III ratio AlGaAs nucleation layers exhibit improved surface morphologies and structural properties. These results were confirmed by optical measurements where it was shown that the best PL response was obtained from GaAs epilayers in which the initial AlGaAs nucleation layers were deposited at a low V/III ratio.