Photo-Hall determination of acceptor densities in n-type HgCdTe

A comprehensive photo-Hall investigation of compensation densities in n-type Hg1−xCdxTe (0.224<x<0.235) is reported. The technique consists of measuring the low-temperature electron mobility as a function of optically excited carrier density. Pulses of 25-μs duration from a CO2 laser yield excess electron-hole plasma densities of between 1013 and 1016 cm−3. At low excitation levels the mobility increases due to the neutralization of ionized acceptors by photoexcited holes, while at higher excitation levels the mobility slowly decreases due to electron-hole scattering. By comparing to a detailed theory for electron transport in photoexcited narrow-gap semiconductors, the density of compensating acceptors NA can be accurately determined. The theory is generalized to account for multi-ion scattering, carrier heating, surface conduction, and inhomogeneous excitation. Experimental refinements significantly extending the range of narrow-gap n-type samples for which compensation densities may be determined are discussed. The present study demonstrates the broad applicability of the technique by determining NA for samples with compensation ratios between 0.09 and 0.96 and with both single and double acceptors.