Very long wavelength infrared (VLWIR, λc approximately 20 to 50 μm) HgTe/HgCdTe superlattices were grown by molecular beam epitaxy (MBE). The layers were characterized by means of X-ray diffraction and Fourier transform infrared spectroscopy. Photoconductive interdigitated electrode detectors for heterodyne applications in the Far-infrared wavelengths (FIR) regions were designed and fabricated. Spectral response measurements exhibit the ability of these detectors to function in the long wavelength (LWIR) to VLWIR regions. Detectivity observed at 77 K is very encouraging and could be enhanced further at lower operating temperatures.
The growth and characterization of Au-doped HgCdTe layers on (211)B CdTe/Si substrates grown by molecular beam epitaxy reported. The electrical properties of these layers studied for diffusion are presented. For ex-situ experiments, thin Au layers were deposited by evaporation and annealed at various temperatures and times to investigate the p-type doping properties and diffusion of Au in HgCdTe. The atomic distribution of the diffused Au was determined by secondary ion mass spectroscopy. We found clear evidence for p-type doping of HgCdTe:Au by in-situ and ex-situ methods. For in-situ doped layers, we found that, the Au cell temperature needs to be around 900°C to get p-type behavior. The diffusion coefficient of Au in HgCdTe was calculated by fitting SIMS profiles after annealing. Both complementary error functions and gaussian fittings were used, and were in full agreement. Diffusion coefficient as low as 8x10-14cm2/s observed for a sample annealed at 250°C and slow component of a diffusion coefficient as low as 2x10-15 cm2/s observed for a sample annealed at 300°C. Our preliminary results indicate no appreciable diffusion of Au in HgCdTe under the conditions used in these studies. Further work is in progress to confirm these results and to quantify our SIMS profiles.
Specially designed mercury cadmium telluride (Hg1-xCdxTe) p-ν-n+ heterostructures were grown by molecular beam epitaxy (MBE) on CdTe/Si and CdZnTe (211)B-oriented substrates for infrared photo-detector operation at near room temperature. Growth of this structure requires precise control over the crystal quality, compositional profiles, and donor and acceptor doping levels. The doping levels and density of Shockley-Read-Hall centers in the absorber layer must be low enough to realize the benefits of Auger suppression under non-equilibrium device operation. In order to avoid possible contamination from chemical compounds used in traditional substrate mounting methods, non-contact (In-free) substrate mounting was used to grow the structures. High-energy electron diffraction (RHEED) was implemented to develop a substrate thermocouple temperature ramping curve that maintains a constant epilayer temperature. The structures were characterized by FTIR, x-ray diffraction, and temperature dependent Hall measurements. High operating temperature (HOT) detectors were fabricated on these materials and showed good room-temperature response.
We have carried out basic research on the extrinsic p-type doping of mercury cadmium telluride epilayers grown by molecular beam epitaxy. The doping is performed with elemental arsenic and gold sources. HgCdTe epilayers of CdTe mole fraction in the range of the long-wavelength and mid-wavelength infrared were grown on (211)B CdTe/Si and CdZnTe substrates. The van der Pauw technique was utilized to study the temperature dependent Hall effect characteristics of the grown epilayers and the photoconductive decay method was used to obtain minority carrier lifetime data. Activation annealing of As at different temperatures was performed. P-type conversion of As doped samples at lower than conventional annealing temperatures was achieved. The influence of the annealing conditions on the Hall effect characteristics of the grown epilayers were studied. As activation in HgCdTe is also studied in the annealing experiments and compared to the current As activation models. We studied the surface and the bulk properties of our p-type doped samples by minority carrier lifetime measurements. Gold doping was achieved by deposition of Au on and its diffusion into samples.
We also investigated the effects of vacancies on the mobility of Au dopants in the HgTe lattice by ab-initio pseudo-potential methods. For this study, we first determined the smallest supercell that will produce reliable results. Then total energy calculations were performed on supercells with nearest neighbor, 2nd nearest neighbor, 3rd nearest neighbor, etc. vacancies relative to Au sites.
II-VI intrinsic very long wavelength infrared (VLWIR, λc~20 to 50 μm) materials, HgCdTe alloys as well as HgCdTe/CdTe superlattices, were grown by molecular beam epitaxy (MBE). The layers were characterized by means of X-ray diffraction, conventional Fourier transform infrared spectroscopy, Hall effect measurements and transmittance electron microscopy (TEM). Photoconductor devices were processed and their spectral response was also measured to demonstrate their applicability in the VLWIR region.
The annealing and electrical properties of extrinsic in situ doped mercury cadmium telluride epilayers grown by molecular beam epitaxy (MBE) on B CdTe/Si and CdZnTe substrates are studied. The doping is performed with an elemental arsenic source. HgCdTe epilayers of CdTe mole fraction in the range of mid-wavelength IR are grown at substrate temperatures of 175-185 degrees C. The temperature dependent Hall effect characteristics of the grown samples are measured by the van der Pauw technique. A magnetic field of up to 0.8 T is used in these measurements. The analysis of the Hall coefficient in the temperature range of 40-300 K with a fitting based on a three-band non-parabolic Kane model, a fully ionized compensating donor concentration, and tow independent discrete acceptor levels is reported. Both as-grown and annealed samples are used in this study. All of the as-grown samples showed-type characteristics whereas annealed samples showed p-type characteristics. Activation annealing at different temperatures was performed. Conversion to p-type at lower than conventional annealing temperatures was achieved. Theoretical models are utilized to understand the dependence of the activated arsenic concentration on the annealing temperature.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.