Research On MOCVD Growth And Opto-electric Characterization Of Antimonide Infrared Detection Materials

Antimonide superlattices are promising for infrared photodetector applications because of their broken-gap band alignment. In comparison to conventional infrared material Hg Cd Te, antimonide superlattices are more mechanically robust, flexibility in detection wavelength by band gap engineering, have reduced tunneling currents, and can use strain to suppress Auger recombination. Antimonide superlattices have drawn considerable interests in recent years and proved to be a prime candidate for the third generation imaging. Reported antimonide superlattice photodetectors are mostly grown by molecular beam epitaxy（MBE）, while reports on the metal organic chemical vapor deposition（MOCVD） growth of antimonide superlattice detector structures are quite scarce in the literature at present. It is well known that MOCVD method has many advantages such as growth process is easier to control and operate, mass production and low cost. In this thesis, MOCVD growth of mid-wavelength infrared（3-5μm） antimonide superlattices were systematically investigated, including interface design, optimization of material growth, characterization and analysis, as well as the device fabrication. The main results are summarized as follows:We have grown Ga Sb buffer layer on Ga As（001） substrate by three-step method. i. e. a thin low temperature Ga Sb nucleation layer, annealing, then followed by a high temperature metamorphic Ga Sb layer. The best Ga Sb buffer layers are obtained and confirmed by atomic force microscope（AFM） and high resolution x-ray diffraction（HRXRD）. The surface root-mean square（RMS） roughness is about 0.5 nm and the full width at half maxima of the HRXRD rocking curve is only 172 arc sec. On the basis of the high quality Ga Sb buffer layer, we deposit a series of In As/Ga Sb superlattices using "exchanged interfaces". HRXRD, AFM and micro-Raman were used to characterize the grown structures. Then micro-Raman scattering from In As/Ga Sb superlattice was performed over the temperature range from 77 K to 357 K. The first-order temperature coefficients of the SL LO and the IF modes were observed to be-0.01674 cm-1/K and-0.01552 cm-1/K, respectively.The main problems in the growth of In As/Ga Sb by MOCVD are complicated interface design. We show that unlike the MBE growth where an interface In Sb layer was found to greatly improve the structural properties of the superlattices. Because of higher growth temperature in MOCVD that an interface In Sb layer could not improve the structural properties of the superlattices. we need to design novel interface structure. This is a huge challenge for In As/Ga Sb superlattices grown by MOCVD. Furthermore, low minority carrier lifetime, resulting from Ga-related trap levels that cause Schockley-Read-Hall（SRH） recombination, which seriously restrict the performance of detector. In order to overcome these limitations, this dissertation work focuses on In As/In As Sb superlattices, another promising alternative for infrared detector applications due to possible lower SRH recombination and the absence of gallium, which simplifies the superlattice interfaces and growth processes.A series of In As/In As Sb superlattices grown using MOCVD on Ga Sb substrates were designed for the mid-wavelength infrared（MWIR） spectral ranges. Detailed characterization using HRXRD, AFM, photoluminescence（PL）, and spectral photoconductivity revealed the excellent structural and optical properties of the MOCVD materials. In order to improve the superlattices materials qualities, we investigate the impact of growth temperature, post growth annealing and V/III ratio on the structural and optical properties of In As/In As Sb superlattices grown by MOCVD. The results demonstrate that the optimal growth temperature is 500 ℃ and post growth annealing（550 ℃, 30 min） can substantial increase the photoresponse. The Sb composition is found to vary non-linearly with substrate temperature and V/III ratios.We investigate the excitation power and temperature-dependence of the PL emission from the MWIR In As/In As Sb superlattices grown by MOCVD. The Varshni and Bose-Einstein parameters determined for energy gap extracted from temperature dependent PL spectra by a fitting procedure are shown. Our results may be useful for further experimental and theoretical studies on the optical properties of In As/In As Sb superlattices detectors. Strong carrier localization inside the In As/In As Sb superlattices have been observed together with the maximum carrier localization energy between 4.9-6.3 me V. It was found that the radiative recombination is dominated by excitons trapped in disorder and interface defects at low temperature. Whereas, at higher temperature, free-exciton radiative recombination occurs. Furthermore, the observed temperature dependent photoluminescence quenching is ascribed to the ionization of bound excitons at low temperatures and the thermal recombination by interface disorder and defects or Sb clusters might be the main quenching channel for high temperature luminescence. As a result of carrier localization, long optically measured carrier lifetimes in In As/In As Sb T2 SLs do not guarantee good detector performance. The carrier localization effect needs to be taken into account for a proper design and evaluation of In As/In As Sb photodetectors. So we introduce the method that can remove or weaken undesired carrier localization. We observed that carrier localization was almost completely removed by annealing（550 ℃, 30 min）.Mid-wave In As Sb n Bn detector on Ga Sb substrate grown by MOCVD designs with In PSb barrier layer have been investigated. Single pixel devices with square mesas of 400×400 μm2 are fabricated utilizing standard optical photolithography. Various simple characteristics of the devices were then measured. The results indicate that the cut-off wavelengths of the In As Sb n Bn detector at 77 K and 300 K are 4.29 μm, 5.35 μm, respectively. Detector normalized blackbody detectivities are 1.2×10⁹ cm?Hz^1/2 W^-1 at 77 K and 3.5×10⁸ cm?Hz^1/2 W^-1 at 300 K.