Photoluminescence in heavily doped GaAs. II. Hydrostatic pressure dependence

The photoluminescence at the direct $E_0$ gap of heavily doped $p$- and $n$-type GaAs has been measured as a function of hydrostatic pressure using a diamond anvil cell. In $p$-GaAs the emission at $E_0$ is still observed for pressures above that at which the material becomes indirect. The intensity of the emission at very high pressures normalized to that of zero pressure can be related to the radiative recombination and the intervalley scattering times. From the pressure dependence of the intensity, besides the pressure coefficient of the $X_1^c$ minima, an average scattering time for transitions from ${\Gamma }_1^c$ to $X_1^c$ is obtained. Luminescence at the indirect gap $X_1^c-{\Gamma }_8^v$ was observed in GaAs with 1.6 × ${10}^{18}$ holes ${\mathrm{cm}}^{-3\mathrm{}}$ for pressures between 40 and 55 kbar. The $E_0$ gap, obtained from luminescence measurements, shows at room temperature the same sublinear behavior as a function of pressure as was reported by Welber et al. At low temperatures ($T=120\mathrm{}$ K). however, we measured a linear pressure dependence. The corresponding linear pressure coefficient is 30% lower than that at room temperature. In $n$-GaAs the linewidth of the emission changes drastically with increasing pressure; the emission disappears when the lowest gap becomes indirect. Both phenomena are due to the transfer of free electrons from ${\Gamma }_1^c$ to $X_1^c$. The linear pressure coefficient of the luminescence lines is smaller than for the $p$ samples because of the pressure dependence of the Burstein-Moss shift.