Concentration-dependent absorption and spontaneous emission of heavily doped GaAs

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Abstract
A model for the calculation of the absorption and emission spectra for GaAs at carrier concentrations in excess of 1×1018 cm−3 is described. This model utilizes a Gaussian fit to Halperin‐Lax band tails for the concentration‐dependent density of states and also includes an energy‐dependent matrix element. The calculated absorption and emission spectra are compared to previous experimental results. All results are for 297 K. For p‐type GaAs, the agreement is very good. The concentration dependence of the effective energy gap is obtained and can be expressed as Eg (eV) =1.424−1.6×10−8 [p (cm−3)]1/3. The concentration‐dependent thermal equilibrium electron‐hole density product n0p0 and the radiative lifetime τr are calculated for p‐type GaAs. The value of n0p0 increases from the low‐concentration value of 3.2×1012 cm−6 to 1.2×1013 cm−6 at p=1.6×1019 cm−3. This value of n0p0, together with the thermal generation rate obtained from the experimental absorption coefficient, gives τr as 0.37 nsec at p=1.6×1019 cm−3.

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