Highly lattice-mismatched epitaxy for III-V/Si integration
Date of Issue2018-02-06
School of Electrical and Electronic Engineering
Indium antimonide (InSb) is a competitive semiconductor for the applications in high electron mobility transistor and mid-infrared photodetector. Integration of InSb on GaAs and Si substrates is promising for higher performance of the devices and lower cost of fabrication, and becomes an important component of opto-electronic integrated circuits. Therefore, much effort has been made to investigate the novel heteroepitaxial approaches to overcome the high lattice mismatch (14.6% for InSb/GaAs and 19.3% for InSb/Si) and different crystal structures between InSb and Si. The thesis focuses on the integration of InSb with Si using solid-state molecular beam epitaxy (MBE) system. First, interfacial misfit (IMF) array was intentionally formed at the InSb/GaAs interface to accommodate the lattice mismatch via surface anion exchange. The relationship between the growth temperature and the formation of IMF was investigated. Transmission electron microscope (TEM) images of the sample grown at 310 °C demonstrated an IMF array consisting of 90° misfit dislocations distributed uniformly along the interface and their separation (3.2 nm) agreed well with the calculated result. Growth temperature above 310 °C suppressed the surface anion exchange to impede the formation of IMF array. Below 310 °C, island coalescences resulted in the formation of threading dislocations. Further optimization of growth process has been focused on two areas: 1) pre-growth Sb reconstructions; and 2) in situ thermal annealing. Sb atoms have three kinds of reconstruction on GaAs surface and III-Sb (GaSb and InSb) layers grew on GaAs with different pre-growth Sb reconstructions. Our simulation demonstrated that the x-ray reciprocal space map (RSM) can be employed to characterize the distribution of misfit dislocations in the IMF array. The results of RSM showed pre-growth (2×8) Sb reconstruction promoted the formation of 90° misfit dislocations in an IMF array. The highest carrier mobility of III-Sb layers was achieved in the III-Sb layers grown on GaAs with pre-growth (2×8) Sb reconstruction. The optimized anneal process was 5 minutes at 590 °C for GaSb and 15 minutes at 420 °C for InSb, respectively. Compared with asgrown III-Sb layers, the lower density of threading dislocations, flatter surface and higher carrier mobility were observed in the annealed samples. We confirmed that the annealing also improved the photoresponsivity of GaSb and InSb photoconductors grown on GaAs. To realize the integration of InSb on Si, GaAs buffer was grown on Ge-on-Si substrates with 6° offcut followed by InSb grown on GaAs via IMF array. An InSb p-i-n photodetector was developed based on this structure. An electron barrier layer was inserted into the conventional architecture of p-i-n photodetector to suppress the dark current. The electrical and optical properties of the photodetector were investigated. The photodetector owned a cutoff wavelength of about 5.3 μm at 80 K and the cutoff wavelength was found to increase with increasing temperature. The 80 K detectivity of the photodetector was 8.8×109 cmHz1/2W-1 at 5.3 μm with the quantum efficiency of 16.3 %. Another approach of the integration of InSb on Si through an AlSb/GaSb buffer was also investigated. In this buffer, GaSb was grown on Si using IMF array to avoid the formation of threading dislocations and InSb quantum dots (QDs) were grown on AlSb surface to decrease the density of microtwins. TEM images showed uniform IMF array existed at the GaSb/Si and QDs nucleated at the sites microtwins to terminate them. AlSb and GaSb were respectively applied on the top of the buffer layer to provide a surface for the growth of InSb. InSb on AlSb surface demonstrated higher crystal quality and electron mobility than InSb on GaSb surface. Moreover, the photoresponsivity in InSb photoconductor on AlSb was higher than that on GaSb.
DRNTU::Engineering::Electrical and electronic engineering::Semiconductors