MBE growth and device processing of MWIR HgCdTe on large area Si substrates

Abstract

The traditional substrate of choice for HgCdTe material growth has been lattice matched bulk CdZnTe material. However, as larger array sizes are required for future devices, it is evident that current size limitations of bulk substrates will become an issue and therefore large area Si substrates will become a requirement for HgCdTe growth in order to maintain the cost-efficiency of future systems. As a result, traditional substrate mounting methods that use chemical compounds to adhere the substrate to the substrate holder may pose significant technical challenges to the growth and fabrication of HgCdTe on large area Si substrates. For these reasons, non-contact (indium-free) substrate mounting was used to grow mid-wave infrared (MWIR) HgCdTe material on 3″ CdTe/Si substrates. In order to maintain a constant tepilayer temperature during HgCdTe nucleation, reflection high-energy electron diffraction (RHEED) was implemented to develop a substrate temperature ram** profile for HgCdTe nucleation. The layers were characterized ex-situ using Fourier transform infrared (FTIR) and etch pit density measurements to determine structural characteristics. Dislocation densities typically measured in the 9 10⁶ cm⁻² to 1 10⁷ cm⁻² range and showed a strong correlation between ram** profile and Cd composition, indicating the uniqueness of the ram** profiles. Hall and photoconductive decay measurements were used to characterize the electrical properties of the layers. Additionally, both single element and 32 32 photovoltaic devices were fabricated from these layers. A RA value of 1.8 10⁶-cm² measured at −40 mV was obtained for MWIR material, which is comparable to HgCdTe grown on bulk CdZnTe substrates.