Growth of InAs/GaAs short-period strained-layer superlattices by molecular beam epitaxy

A study of InAs/GaAs short period strained layer superlattices (SPSLSLs) growth by molecular beam epitaxy (MBE) is presented. The primary objective was to improve the low-field two-dimensional electron gas (2DEG) mobility of an InAs/GaAs SPSLSL channel high electron mobility transistor (HEMT).; A detailed study of the SPSLSL growth using in situ reflection high energy electron diffraction (RHEED) was performed. RHEED observations were used to provide a qualitative analysis of the SPSLSL structures grown. The structural quality of the InAs/GaAs SPSLSL is ultimately limited by the effects of In segregation, which is the direct result of an atomic exchange reaction that occurs when GaAs is deposited on InAs. Suppression of indium (In) segregation can be achieved by using low substrate temperatures and high As{dollar}sb4{dollar} flux during SPSLSL growth. From RHEED observations, it was found that at a substrate temperature of 420{dollar}spcirc{dollar}C, In segregation is effectively suppressed at As{dollar}sb4{dollar} fluxes sufficient to maintain an As-stable surface during SPSLSL growth. To suppress In segregation at higher SPSLSL growth temperatures, As{dollar}sb4{dollar} fluxes in excess of that necessary to maintain As-stable growth were needed. Monolayer completion was also found to be key in reducing In segregation.; The effect of growth conditions (i.e. substrate temperature and arsenic flux) on the 2DEG low-field mobility of the SPSLSL channel HEMT was investigated. It was found that despite the improved interfacial quality of SPSLSLs grown at lower substrate temperatures, the electrical quality was degraded. For SPSLSL channel HEMTs grown at 520{dollar}spcirc{dollar}C under excess arsenic conditions, 2DEG low-field mobilities measured at 300 K and 77 K of 7,600 and 33,000 cm{dollar}sp2{dollar}/V-sec, respectively, were routinely obtained. This represents a 10% and 70% improvement in mobility at 300 and 77 K, respectively, when compared to the corresponding InGaAs alloy. In one sample grown, a remarkable improvement in the 2DEG low field mobility was obtained. A low-field 2DEG mobility of 10,000 cm{dollar}sp2{dollar}/V-sec was measured at room temperature for a SPSLSL channel HEMT grown at 520{dollar}spcirc{dollar}C under an excess arsenic flux. This value is the highest room temperature low-field mobility ever observed for GaAs-based materials. More important, however, is the fact that the mobility obtained exceeds the theoretically predicted room temperature mobility in GaAs limited only by polar optical phonon scattering.; A theoretical model of the scattering mechanisms in a SPSLSL channel HEMT is proposed based on scattering from ionized impurities, interface charge, and polar optical phonons. The low temperature 2DEG mobility is shown to be limited by interface charge scattering due to the multiple interfaces present in the SPSLSL system. Using this model, excellent agreement was found between the theoretical and experimental 2DEG mobility versus temperature profile.