R. Arès

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.

Growth mechanisms in atomic layer epitaxy of GaAs

We present a study of the different mechanisms governing the growth of GaAs by atomic layer epitaxy (ALE). The gallium precursors such as trimethylgallium (TMGa), triethylgallium (TEGa), and trisneopentylgallium (TNPGa) were characterized and compared during ALE by in situ reflectance difference spectroscopy (RDS). A fundamental difference is observed in the RDS behavior after the alkyl exposure between self-limiting and non-self-limiting precursors. A transient is observed during the purge following alkyl exposure for both self-limiting sources, (TMGa and TNPGa), and is absent with TEGa. This is attributed to the presence of methyl radicals when using self-limiting precursors. Atomic force microscopy measurements of the surface morphology show that a non-self-limiting surface prepared with TEGa has droplets forming on it. In contrast, TMGa and TNPGa show well-defined terraces without droplets. RDS real-time measurements show that Ga incorporating on the c(4×4) surface first reacts with the As in the top ...

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.

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.

Time-resolved reflectance difference spectroscopy of InAs growth under alternating flow conditions

We report a time-resolved reflectance difference spectroscopy (RDS) study of the growth of InAs during alternating flow conditions typical of atomic layer epitaxy (ALE). The precursors used were trimethylindium (TMIn) and tertiarybutylarsine (TBAs). For ALE growth we observe that the InAs surface remains As-rich for an appreciable fraction of the 1 monolayer (ML) TMIn pulse. This is similar to results obtained for the growth of GaAs by ALE using trimethylgallium. Three distinct RDS spectra are observed, two corresponding to As-rich phases, and one which is In-rich. In both InAs and GaAs the extra As layer appears to play a key role in maintaining self-limiting behaviour.