Science and applications of III-V graded anion metamorphic buffers on InP substrates

High-In InGaAs and InAs material systems are of extraordinary interest for applications of high-speed and infrared devices due to their large carrier mobilities and small band-gaps. However, there is no lattice-matched standard substrate technology for high-In InGaAs and InAs currently and lattice-mismatched direct growth usually leads to high density of threading dislocations, which significantly degrade device performance, particularly minority carrier devices. To obtain device-quality materials, metamorphic graded buffers are required between the substrate and the high-In InGaAs and InAs layer to accommodate the lattice mismatch and filter the dislocations. In other words, metamorphic graded buffers are equivalent to a virtual substrate with tunable lattice constant, supporting materials with desired lattice constant on lattice mismatched substrates. This technique shows the promise of removing the constraints imposed by standard substrates and realizing lattice engineering in semiconductor technology.; Conventional metamorphic graded buffers grown on GaAs and InP substrates are mixed cation materials, which change the group III composition to adjust the lattice constant of the buffers. However, mixed anion graded buffers have potential advantages over mixed cation graded buffers because, during the growth of mixed anion materials, the control of the growth rate is decoupled from that of the chemical composition. This work focuses on the science and applications of metamorphic mixed anion InAsP graded buffers grown on InP substrates by solid source molecular-beam epitaxy (MBE). The main research activities include the comparison of structural properties between mixed anion and mixed cation graded buffers, the minority carrier lifetime study on InGaAs double heterostructures grown on InP using InAsP graded buffers, and the investigation of high-quality InAs grown on InP using metamorphic InAsP graded buffers.; The first part of this research is the comparison of InAsP (mixed anion) and InAlAs (mixed cation) graded buffers. InAsP and InAlAs step-graded buffers were designed and grown with identical buffer thickness and lattice mismatch (∼ 1.3%) with respect to InP substrates. Although the strain relaxation of both buffers were determined to be close to 90% by high-resolution x-ray diffraction, InAsP graded buffers showed smoother surface morphology and lower threading dislocation density compared to InAlAs graded buffers. Atomic force microscopy reveals that the surface roughness (RMS) of InAsP and InAlAs graded buffers were 2.2 nm and 7.7 nm, respectively. With cross-sectional and plan-view transmission electron microscopy, the threading dislocation density was measured to be ∼ 4x106 cm-2 for InAsP graded buffers, which is much lower than that for InAlAs graded buffers (> 1x107 cm-2).; Minority carrier lifetime is a very important parameter for the material quality evaluation and better understanding of carrier loss mechanisms. To obtain the information of the minority carrier lifetime, InGaAs double heterostructures (DH) were grown on InAsP and InAlAs graded buffers. Ultra-high photoconductive decay (PCD) was performed on to measure minority carrier lifetimes. Very high carrier lifetimes (4-5 micros) were observed for the InGaAs DH with InAsP graded buffers whereas only ∼ 0.5 micros for that with InAlAs graded buffers, indicating that high quality of the InAsP graded buffers translates into high electronic quality InGaAs with high carrier lifetime. The dependence of lifetimes on the thickness of DHs revealed the excellent InAsP/InGaAs interface quality. In this study, a model combine with wavelength dependent analysis of the initial nonlinear decay observed in PCD data is also presented to explain the possible role of carrier diffusion in PCD characterization.; In view of our previous work of high quality InGaAs/InAsP/InP, it is very promising to extend InAsP graded buffers all the way to support high device qua...