Conduction-band offset determination in GaAs-AlxGa1−xAsthrough measurement of infrared internal photoemission

Internal photoemission from a two-dimensional electron gas formed at GaAs-${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ selectively doped heterojunctions has been measured for $x=0.25, 0.28, 0.36, \mathrm{and} 0.38$. The photoresponse increases rapidly with the angle of incidence of the light, indicating that it results from intersubbandlike transitions. We have developed a model for the photoemission, and used the measurement to determine the conduction-band offset. We find values of $Q_e=\frac{\Delta E_c}{\Delta E_G}$ of 0.79, 0.76, 0.67, and 0.65, respectively, for the $x$ numbers stated above, showing a smooth decrease with $x$.