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Intervalence band absorption in semiconductor laser materials

Intervalence band absorption (IVBA) has been proposed as a possible cause of the temperature sensitivity of threshold currents in the longer-wavelength semiconductor lasers used for optical fibre communications. In view of the potential importance of this effect, IVBA coefficients for the spin split off-heavy hole band transition have been evaluated for GaAs, Ga0.47In0.53As and Ga0.28In0.72As0.6P0.4 for temperatures in the range 150<T<400K and hole concentrations from 0.75-3*1018 cm-3. The model used incorporates band structure and momentum matrix elements based on a Chelikowsky and Cohen (1976) pseudopotential calculation for 21 k-space directions in an irreducible segment of the Brillouin zone. Absorption at the band-gap wavelength is found to be greatest in the ternary material which, along with GaAs, exhibits a small temperature dependence, the temperature coefficient of absorption becoming negative at high temperatures. The temperature dependence of the quaternary material is more marked, but the absorption coefficient is small (for p=1018 cm-3) at all temperatures considered. Absorption coefficients for all materials exhibit an approximately linear dependence on concentration.