A new p-n junction formation method on p-HgCdTe by indium rapid thermal diffusion and a new plausible structure of two color IR detector are proposed.
Rapid thermal diffusion of indium into HgCdTe (x=0.30) is studied over the temperature range of 100 - 200 ℃, for 5 - 600 seconds. It is observed that there are two diffusion components, the first one being an erfc function fitted atomic component and the other being an exponentially fitted fast component. From the Arrhenius plot, the diffusion coefficients of indium by RTD in HgCdTe (x=0.30) were fitted by $D(T) = 1.45 × 10^{-2} \exp(-0.772(eV)/kT) ㎠/s$. The activation energy is 0.772 eV. From the differential Hall and conductivity measurements at 77K, it is observed that not all of the diffused indium is activated as donors and that the portion of activated indium depends heavily on the indium concentration.
Large suppression of reverse bias leakage current is archived in the RTD photodiodes in comparison with ion implanted HgCdTe photodiode. The suppression of defects generation in junction formation by RTD might give the p-n junctions with reduced traps, resulting the suppression of reverse bias leakage current. The extracted minority carrier lifetime from plot of R0A versus 1000/T obtained from RTD diode is 6 times larger than that from ion implanted diodes. This means that the trap density in the RTD diodes is reduced by 6 times. This result suggest that junction formation by RTD is more advantageous than junction formation by ion implantation for the future high density IRFPA.
We propose a new n-p-N structure simultaneously and independently operable two color (MW/LWIR and SW/MWIR combination) detector. The proposed two color detector has the back-to-back diode structure of the n-p-N-HgCdTe on CdZnTe substrate. The potential barrier in p-N heterojunction plays critical role in that it prevents photogenerated minority carriers in p-HgCdTe from diffusing to N-HgCdTe. The heterojunction analysis with device simulator predicts that the potential barrier height is as large as at thermal equilibrium at 77 K in the heterojunction of $p-Hg_{0.78}Cd_{0.22}Te/ N-Hg_{0.69}Cd_{0.31}Te$ with the hole and the electron concentrations of $1 × 10^{16} cm^{-3}$ and $5 × 10^{15} cm^{-3}$ respectively and 13.4kt for the case of $p-Hg_{0.69}Cd_{0.31}Te/N-Hg_{0.636}Cd_{0.364}Te$ with the same doping.
The barrier height of 13.4ktis enough to prevent photogenerated minority carriers in $p-Hg_{0.69}Cd_{0.31}Te$ from diffusing to N- $Hg_{0.636}Cd_{0.364}Te$. It can be observed that the spectral responses of the two photodetectors are well discriminated and negligible spectral crosstalk. Spectral quantum efficiency curve is not remarkable changed with the composition grading width variation from 0 to 2 $\mm$, this indicates small potential barrier change due to composition grading width variation the does not drastically affect the spectral response of the proposed two color detector.
It is confirmed that the proposed two color detector might be truly simultaneously and independently operable, that is, simultaneously and independently detection and integration could be accomplished.
