Growth and defect characterization of low temperature molecular beam epitaxy GaAs

Excess arsenic atoms (∼1%) can be incorporated as antisite (As _Ga) defects occupying the normal Ga sublattice, when GaAs is grown at low substrate temperature (LT-GaAs) by molecular beam epitaxy (MBE). The existence of mid-gap states related to a large concentration of excess arsenic renders LT-GaAs with high resistivity and very short carrier lifetime (<1ps). LT-GaAs has been widely used to improve the performance of electronic devices and design novel ultrafast optoelectronic devices.; The substrate temperature strongly influences As_Ga incorporation during growth. Using the unique diffuse reflectance spectroscopy (DRS), we evaluated the substrate temperature transients caused by the radiation heating from hot effusion cells. The characteristic As_Ga sub-bandgap absorption was studied in situ in a wide temperature range. We found that the As_Ga defect absorption is nearly temperature independent and its incorporation is uniform during growth. We demonstrated that As _Ga concentration can be measured in situ using DRS.; Beryllium doping can cause both electrical and strain compensation with As_Ga, which benefits LT-GaAs stability. It was found that the low temperature growth process reduces Be surface segregation and diffusion, which enables us to achieve ultrahigh hole concentration (∼8 × 10 20/cm3) with sharp profiles. The interaction between Be dopants and the supersaturated native defects, i.e., As_Ga and Ga-vacancy (V_Ga), also leads to a decrease of Be diffusion during post-growth annealing. It was also shown that As_Ga concentration is significantly reduced by heavily silicon doping (>1 × 1019 /cm3). Record-breaking free electron concentration (2.1 × 1019/cm3) has been achieved using LT MBE growth of GaAs.; To calculate carrier induced optical nonlinearities, a general approach was described by taking into account of carrier bandfilling, bandgap renormalization and free carrier absorption. Calculations have shown a linear relationship between carrier densities and optical constant changes in a certain spectral range. The transient optical nonlinearities (transmission and reflectance) were measured using a femtosecond laser pump-probe spectroscopy to study the carrier relaxation in LT-GaAs:Be. By changing the charge states of As _Ga, it was identified that the singly positively charged $As+Ga$ is one of the dominant electron trapping centers, with an electron capture cross section of σ_n × 1.3 × 10−15cm2. A set of rate equations were proposed to study the different relaxation channels of photogenerated carriers.; Besides the substrate temperature and the beam fluxes during MBE growth, the doping, especially Be-doping, provides an additional parameter to engineer the properties of LT-GaAs.