Photoconductance measurements on thin InGaN layers

We report photoluminescence (PL), transmission and photoconductance (PC) st udies of InxGa1-xN and GaN alloys grown by metalorganic chemical vapor depo sition. We demonstrate that PC measurements can provide reliable gap estima tes for a large range of film thicknesses in contrast to transmission or ph otoreflectance experiments. We show that PC measurements give the expected classical value for thick GaN layers by using an elementary model for absor ption. They also give the same value as transmission experiments in the cas e of thin InGaN layers. We have performed PL and PC measurements in InGaN l ayers. The comparison between the PL peak and PC measurements gives a direc t access to the Stokes shift. We study the Stokes shift as a function of te mperature. Depending on the particular film, the Stokes shift can be explai ned in terms of localization or the Burstein-Moss effect. Indeed, Hall meas urements show a high electron concentration in some of the films. Thus, our measurements show that very homogeneous InGaN layers with high indium cont ent (22%) can be obtained with a very small Stokes shift and with a very na rrow PL peak. In addition, we give the temperature dependence of the InGaN band-gap. (C) 2000 American Institute of Physics. [S0021-8979(00)03119-4].