Transient carrier decay and transport properties inHg1−xCdxTe

Abstract

The transient decay of large excess-carrier densities was investigated in ${\mathrm{Hg}}_{1-x}{\mathrm{Cd}}_x\mathrm{Te} \mathrm{}(x=0.205\mathrm{})\mathrm{}$ at 77 K. Excess carriers were generated by bulk impact ionization in strong electric fields. A strong variation of the carrier lifetime with excess-carrier density was observed in the transient excess-carrier decay. The comparison with calculated values shows that the carrier decay is determined by the Auger recombination process. To our knowledge this is the first observed Auger-dominated transient carrier decay in a semiconductor. A typical Auger-dominated lifetime for carriers at excess-carrier densities not far from thermal equilibrium is 460 nsec for $n_0=9\mathrm{}\times {10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and ${\mu }_H=2.26\mathrm{}\times {10}^5$ ${\mathrm{cm}}^2$/V sec at 77 K. This lifetime decreased to 90 nsec at an excess-carrier density equal to $n_0$. Photoconductivity experiments indicate that the majority-carrier lifetime can be enlarged due to minority-carrier trapping near contacts. This was established in photoresponse measurements with ${\mathrm{CO}}_2$ laser pulses. In addition to this, the Hall mobility was measured and analyzed between 4.2 and 200 K. Calculations for combined ionized-impurity and polar-optical-phonon scattering indicate that above 77 K the polar-optical-phonon scattering limits the mobility. This electron-phonon interaction was calculated taking into account the two-mode behavior of ${\mathrm{Hg}}_{1-x}{\mathrm{Cd}}_x\mathrm{Te}$. The high-field measurements have shown that in electric fields above 150 V/cm impact ionization occurs. Values of the carrier generation rate of ${\mathrm{Hg}}_{0.8}$ ${\mathrm{Cd}}_{0.2}$ Te were deduced from the time dependent $j\left(E\right)\mathrm{}$ characteristics.