An important problem in processing the infrared detector material Hg1−xCdxTe is avoiding undue mercury loss. Here we quantify that loss and apply the information to the annealing of ion implanted Hg1−xCdxTe. We thus extend the work of Takita et al. on Hg loss in HgTe to the ternary Hg1−xCdxTe. The Hg loss is generated with a thermal-pulse annealing system and measured by Rutherford backscattering spectrometry (RBS). The loss rate is studied as a function of temperature, composition, and surface preparation (chemimechanical and contactless polishing). For each set of conditions the data is fit to an Arrhenius equation N⧠ /t=A exp(−ΔE/kT) and the fitting parameters A and ΔE are determined. ΔE ranges from 1.0 to 2.5 eV and A varies from 1023 to 1036 atoms/cm2 s. Channeling RBS was also used to study the effect of thermal pulse annealing on boron implanted material. The rate of change of the minimum yield (χmin) with depth, which can be related to certain types of damage, was consistent with the calculated implant damage profile. A 260 °C 8 s anneal restored the crystal quality to better than the as-received material, as observed by channeling.
The problem of Hg loss from HgCdTe is investigated for rapid thermal processing of device quality material. Outdiffusion of Hg from HgCdTe is characterized by fitting calculated diffusion profiles to measurements by Rutherford backscattering spectrometry (RBS). Fitting parameters used are diffusion length 2(Dt)1/2, and ratio of surface transfer rate to diffusion rate ht/(Dt)1/2. The results of these calculations include an estimation of diffusion coefficient D, surface transfer rate h, Hg concentration profile C(x,t), Hg flux F(t), and total Hg lost Q(t). Measurements were taken over a temperature range of 300 to 400 °C and for Cd compositions of 0.23 and 0.4. Surface transfer rate is found to have a strong dependence on surface preparation and diffusion coefficient is observed to change significantly under large Hg loss conditions. A vacancy pair diffusion mechanism is suggested. This work is intended to aid in establishing guidelines for device fabrication processes.
The effect of 30 MeV electron irradiT i.on op InGaAn LEDs and InGaAs photodiodes was studied. Electron fluxes ranged from 10 e /cm to 1015 e /cm2. The beam profile was measured with an improved scanning wire technique.During irradiation, light output, total current, and temperature were monitored for the LEDs.Responsivity and temperature were monitored for the photodiodes.Spectral characteristics and current -voltage curves were measured before and after irradiations. Changes in photodiode dark current were observed and LED lifetime-damage constant products were computed.
Thermal pulse annealing has been used to modify the near surface of Hg1−xCdxTe. Using anneals of approximately 260°C for seven seconds, the crystal quality of epitaxial HgCdTe surfaces can be improved as observed by MeV He+ ion channeling. Similar anneals have also been used to repair the damage resulting from a 250 keV, 101511 B/cm2 implant into HgCdTe held at LN2. For higher temperatures and/or longer anneals, surface Hg loss is observed. Rutherford Backscattering measurements are used to measure this loss. The resulting loss rate data is described by No= A exp (−ΔE/kT) where A and ΔE depend on the material composition with A = 1029, ΔE = 1.8 eV and A = 1036, ΔE = 2.6 eV for x = 0.23 and 0.4, respectively.
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