Pressure Dependence of the Emission fromGa(As1−xPx)Electroluminescent Diodes

The spontaneous and stimulated emission from $\mathrm{Ga}\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)$ diodes with $0.05<x<\mathrm{}0.37\mathrm{}$ has been measured as a function of hydrostatic pressure up to 7 katm at 77°K. For $x<\mathrm{}0.35\mathrm{}$, the pressure shift of the peak of the incoherent radiation was found to be close to that determined for GaAs. For $x>\mathrm{}0.35\mathrm{}$, the shift decreased and finally reversed, consistent with the identification of the subsidiary edges as lying along $k=\left(100\right)\mathrm{}$. The pressure-induced narrowing of the spontaneous linewidth for lightly doped diodes of small GaP content suggests the correctness of the following model: a degenerate concentration of electrons is injected into the conduction band with the radiative recombination taking place on the $p$-type side of the junction. The absence of such a narrowing for heavily doped diodes points up the importance of band tailing to the spectral width of the emitted radiation. Our experimental results further show that tail states attached to the (100) band edges extend deep into the forbidden gap and affect the emission process for values of $x$ as low as 0.25. From the behavior of the threshold current under pressure, it is concluded that 6400 Å seems to be the practical lower limit for the generation of stimulated emission in $\mathrm{Ga}\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)$ at 77°K.