C. A. Tran

Low‐temperature photoluminescence of epitaxial InAs

Photoluminescence studies as well as reflectance and transmittance measurements were performed on high‐purity epitaxial InAs grown by metal‐organic chemical‐vapor deposition. We report the optical identification of excitonic, donor, and acceptor impurity related transitions at a temperature of 1.4 K. Measurements at higher temperature and in the presence of magnetic fields up to 7 T support these identifications. We find the excitonic band gap at 415.65±0.01 meV according to the minimum in the polariton reflectance feature. The donor–acceptor‐pair and acceptor‐bound exciton transitions for three different acceptors are observed by photoluminescence, and we tentatively associate one of them to a double acceptor formed by a Ga impurity on an As lattice site. A donor‐bound exciton transition is observed with a binding energy of 0.42 meV. The magnetic field dependence yields values of the electron effective mass and g factor of (0.026±0.002)m0 and −15.3±0.2, respectively, in good agreement with values obtaine...

High mobility InAs grown on GaAs substrates using tertiarybutylarsine and trimethylindium

We report transport measurements on a series of high purity InAs epilayers grown on GaAs substrates by metalorganic chemical vapor deposition using tertiarybutylarsine and trimethylindium. Perfectly specular surfaces were obtained by a two step growth method consisting of a 400 °C prelayer followed by deposition of the thick bulk layer at higher growth temperatures. Temperature dependent Hall measurements between 1.8 and 293 K showed a competition between bulk and surface conduction, with average Hall mobilities of up to 1.2×105 cm2/V s at 50 K. Large changes in the temperature dependent transport data are observed several hours after Hall contact formation and appear to be due to passivation of the surface accumulation layer by native oxide formation.

Sharp excitonic photoluminescence from epitaxial InAs

The optically excited luminescence of epitaxial InAs has been studied at 1.4 K, revealing well‐resolved emission lines identified as the exciton–polariton, neutral–acceptor–bound exciton principal and two‐hole transitions, donor–acceptor pair band, and phonon assisted transitions. These features are seen in samples of high purity InAs grown by metalorganic chemical vapor deposition on InAs substrates using tertiarybutylarsine and trimethylindium. Only one acceptor species is observed, having a 1 S3/2–2 S3/2 transition energy of 13.39±0.01 meV, and an acceptor–bound exciton binding energy of 2.11±0.03 meV.

Temperature dependence of photoluminescence in InAsP/InP strained multiple quantum wells

The photoluminescence spectra of InAsP/InP strained multiple quantum wells have been experimentally determined in the temperature range 7–300 K. In order to understand the temperature behavior of the photoluminescence, a theoretical calculation is presented that takes into account the temperature‐induced variations in band gap, carrier effective mass, biaxial strain, and exciton binding energy. The results show that the energy of the transition E1H between the n=1 electron subband and the n=1 heavy‐hole subband changes as a function of temperature, and depends mainly on the evolution of the strained band gap of the InAsP layers. This is because in the temperature range 7–300 K the variations of the electron subband energy and the exciton binding energy are much less than those of the strained band gap, while the variation of the heavy‐hole subband energy can be neglected. These results also explain why, for a lattice‐matched quantum well, the variation of exciton peak energies with temperature follows tha...

Atomic layer epitaxy and structural characterization of InP and InAs/InP heterostructures

We report the growth and structural properties of InP, InAs/InP strained single quantum wells and short‐period InAs/InP strained layer superlattices by atomic layer epitaxy. A self‐limiting growth close to 1 monolayer/cycle has been obtained for InP and for InAs with low substrate temperatures between 350 and 360 °C. The samples were grown on InP (001) substrates and characterized by high resolution x‐ray diffraction, grazing‐incidence x‐ray reflectometry, and Raman spectroscopy. The interference of x‐ray wave fields in the grown structures observed by both types of x‐ray measurements can be used to measure nondestructively the thickness of the deposited films with relatively high precision. High resolution x‐ray diffraction and grazing‐incidence x‐ray reflectometry of the InAs/InP superlattices confirm the periodicity of the structures in agreement with theoretical predictions. Raman spectroscopy shows doublets of folded acoustic modes as well as InAs‐like and InP‐like confined longitudinal optical phono...

Atomic force microscopy study of morphology and dislocation structure of InAs and GaSb grown on highly mismatched substrates

Abstract We have studied the surface morphology and dislocation structure of InAs grown on GaAs or InP substrates and of GaSb grown on GaAs substrates by metalorganic chemical vapour deposition (MOCVD). Atomic force microscopy (AFM) has been used to determine quantitative threading dislocation densities by observing singularities in the atomic terrace structure. All layers were grown using a thin ∼ 100 nm low temperature buffer layer grown at 400°C, which was found to greatly improve surface morphology for all materials combinations studied. The lowest dislocation densities were found for thick GaSb layers on GaAs, with around 1 × 10 6 cm −2 for a 5 μm layer. While somewhat higher levels were observed for InAs (5 × 10 6 cm −2 ), the surface roughness for these films was significantly lower. In all samples the limiting factor for surface roughness is observed to be the formation of hillocks consisting of growth spirals centred on dislocations. We suggest ways in which these data may be used to calculate some fundamental MOCVD crystal growth parameters such as the critical radius for nucleation.

Atomic layer epitaxy of InAs using tertiarybutylarsine

Tertiarybutylarsine and trimethylindium were used as precursors for atomic layer epitaxy of InAs. Self-limiting growth has been observed for a large temperature range between 350–410°C. In-situ reflectance difference spectroscopy was used to study the difference between the As and In self-limiting mechanisms on the InAs surface and also to optimize the growth parameters. Optical and transport properties of InAs grown epilayers show that high purity material can be achieved by atomic layer epitaxy.

Characterization of very high purity InAs grown using trimethylindium and tertiarybutylarsine

The growth of high purity InAs by metalorganic chemical vapor deposition is reported using tertiarybutylarsine and trimethylindiμm. Specular surfaces were obtained for bulk 5-10 μm thick InAs growth on GaAs substrates over a wide range of growth conditions by using a two-step growth method involving a low temperature nucleation layer of InAs. Structural characterization was performed using atomic force microscopy and x-ray diffractometry. The transport data are complicated by a competition between bulk conduction and conduction due to a surface accumulation layer with roughly 2–4 × 1012 cm−2 carriers. This is clearly demonstrated by the temperature dependent Hall data. Average Hall mobilities as high as 1.2 x 105 cm2/Vs at 50K are observed in a 10 μm sample grown at 540°C. Field-dependent Hall measurements indicate that the fitted bulk mobility is much higher for this sample, approximately 1.8 × 105 cm2/Vs. Samples grown on InAs substrates were measured using high resolution Fourier transform photoluminescence spectroscopy and reveal new excitonic and impurity band emissions in InAs including acceptor bound exciton “two hole transitions.” Two distinct shallow acceptor species of unknown chemical identity have been observed.

Strain effects in high‐purity InP epilayers grown on slightly mismatched substrates

The growth of high‐purity InP on various As‐, S‐, and Fe‐doped InP substrates has been investigated using high‐resolution photoluminescence spectroscopy (PL) and high‐resolution x‐ray diffractometry. Substrate induced strains of −7×10−5 or less have been observed using low‐temperature PL. In this way information about the strain dependence of the electronic excited states of the donor bound excitons in InP was obtained. In addition, it was shown that the assessment of variations in substrate lattice parameter can be determined with a resolution of at least 5×10−6 by PL techniques.

Breakdown of self-limiting behaviour in InAsGaAs heterostructures grown by atomic layer epitaxy

Abstract We report on the study of indium incorporation during the growth of monolayer and submonolayer thick InAs GaAs heterostructures grown by atomic layer epitaxy using trimethylindium (TMI), trimethylgallium (TMG), and tertiarybutylarsine (TBA). The incorporation of indium during TMI exposure is shown to differ significantly depending on the nature of the surface it is impinging upon. In the case of an InAs surface exposed to a TMI flux, the total indium coverage increases linearly in the early stages of exposure and saturates at one full monolayer for exposures greater than 3 and 4 s for growth temperatures of 390 and 360°C, respectively. This is in strong contrast with the case of a GaAs surface where TMI exposures of up to 12 s produce incorporation of indium and growth of InAs linearly with time. The amount of indium incorporated in the structures was determined for all samples using dynamical X-ray scattering simulations. At 360°C the total amount of incorporated indium in GaAs was observed to exceed the critical thickness (∼ 2 monolayers), reaching values greater than 3.5 monolayers. Even though indium covers the InAs surface with a rate which increases with temperature, no change in In incorporation is observed in the heteroepitaxy case. These data provide a clear example of the breakdown of self-limiting behaviour for ALE heteroepitaxy.