Energy scaling of compositional disorder in Ga(N,P,As)/GaP quantum well structures

In many-component semiconductor heterostructures photoluminescence (PL) is strongly affected by the disorder potentials caused by compositional fluctuations. We present an experimental study on the temperature-dependent PL in the Ga(N,P,As)/GaP quantum well which indicates the intriguing feature that the energy scale of the disorder decreases with increasing concentration of the fluctuating compositional component (nitrogen). This effect strongly suggests that the impact on the band structure and the effective mass both decrease as the N concentration increases. This conclusion is supported by theoretical estimates using the analytical theory of compositional fluctuations in mixed crystals.

Figure 1

Schematic shapes of the temperature-dependent (a) PL peak position (solid line) and band gap (dashed line), and (b) PL linewidth taking into account the hopping transitions of carriers between the localized states.

Figure 2

Experimentally observed temperature dependencies of (a) the peak energy and (b) the linewidth of the PL emission spectra in Ga(N,P,As)/GaP QW structures with different nitrogen content; (c) corresponding low-temperature spectra.

Figure 3

(a) Nitrogen content dependence of the energy scale of the compositional disorder in Ga(N,P,As)/GaP QW structures as extracted from the experimentally observed peak temperatures corresponding to the maximal Stokes shift and to the maximal PL linewidth (solid circles) in comparison with the estimate from the BAC theory assuming a constant effective mass (dashed line) and taking into account the compositional dependence of the effective mass given by Eqs. (7) and (9) (open circles). Solid lines are the guide to the eyes. (b) Nitrogen content dependence of the parameter $\alpha$, calculated assuming a constant effective mass and applying the BAC theory (dashed line) and the theory of compositional disorder (solid circles). Here, the values of the energy scale of disorder extracted from the temperature-dependent PL measurements have been used. The solid line shows the interpolated $\alpha \propto x_{\mathrm{N}}^{-0.64}$ power dependence.

Figure 4

$\alpha =\partial E_{\mathrm{c}}/\partial x_{\mathrm{N}}$ as a function of the nitrogen and phosphor concentrations in strained Ga(N,P,As)/GaP QW structures, calculated using the BAC theory.

Figure 5

(a) Exciton effective mass $m$ as a function of the nitrogen and phosphor concentrations in strained Ga(N,P,As)/GaP QW structures, calculated using Eqs. (7) and (9); (b) the values of the effective mass, which provide exact agreement between the energy scales of disorder calculated using the analytical theory of compositional disorder and that extracted from the experimentally observed PL features (solid circles). For comparison purpose the nitrogen content dependencies of the effective mass calculated from Eqs. (7) and (9) for fixed values of phosphor content are also shown by open circles.