MBE growth and device applications of lattice-matched and strained heterostructures on (n11)-oriented and patterned substrates

The epitaxy of lattice-matched and strained semi-conducting films on patterned and misoriented substrates has led to new growth phenomena, material properties and device applications. Our work on InP- and GaAs-based heterostructures on (111)- and (311)-oriented substrates and strained heterostructures on planar and patterned (small area) substrates is described in this paper. The possibility of reliable and reproducible p-type doping of (311)A GaAs by Si during molecular-beam epitaxial growth and the application of such doping in the realization of high-performance electronic devices have been investigated. It is seen that p-type doping up to a free hole concentration of 4 × 10¹⁹ cm⁻³ is obtained at low ( 500°C) growth temperature and high As₄ flux. The incorporation of Si atoms into electrically active As sites is at least 95%. n-p-n heterojunction bipolar transistors grown by all-Si doping exhibit excellent current voltage characteristics and a common emitter current gain β = 240. Doped channel p-type heterojunction field-effect transistors have transconductance g_m = 25 mS/mm. We have experimentally and theoretically studied piezo-electric field effects in InP-based In_xGa_{1 − x}As/In_0.52Al_0.48As pseudomorphic quantum wells grown by molecular-beam epitaxy on (111)B InP substrates. The electro-optic coefficients of this material were measured and found to be much larger than that of GaAs. We have also investigated the consequences of altered growth modes on the epitaxy of highly strained InGaAs on patterned small area (001) GaAs substrates. Al_0.15Ga_0.85As/In_0.25Ga_0.75As pseudomorphic modulation-doped field-effect transistors and strained In_xGa_{1 − x}As/GaAs p-i-n photodiodes have been fabricated on patterned (100)-GaAs substrates and characterized. Compared with devices made on planar substrates, small area growth improves the dc transconductance by 40% and current gain cutoff frequency by 50% in the transistors. Photodiodes grown in small recesses (30 μm) exhibit 2–4 times higher quantum efficiency than those on planar substrates.