AVS 51st International Symposium
    Semiconductors Wednesday Sessions
       Session SC-WeA

Paper SC-WeA6
Energy Gap and Stokes-like Shift in Cubic In@sub x@ Ga@sub 1-x@N Epitaxial Layers

Wednesday, November 17, 2004, 3:40 pm, Room 304C

Session: Narrow Gap Semiconductors
Presenter: J. Soares, University of Illinois at Urbana Champaign
Authors: DG Pacheco-Salazar, University of Sao Paulo, Brazil
J.R.L. Fernandez, University of Sao Paulo, Brazil
J. Soares, University of Illinois at Urbana Champaign
J.R. Leite, University of Sao Paulo, Brazil
F. Cerdeira, University of Campinas, Brazil
E.A. Meneses, University of Campinas, Brazil
S.F. Li, University of Paderborn, Germany
O. Husberg, University of Paderborn, Germany
D.J. As, University of Paderborn, Germany
K. Lischka, University of Paderborn, Germany
Correspondent: Click to Email
Group-III nitrides have been intensively investigated due to their recent applications in optoelectronic and electronic devices. The light emission mechanism of efficient blue-green-ultraviolet LED and laser diodes based on these materials is still object of investigation, and several works have been carried out recently on the optical properties of the In@sub x@Ga@sub 1-x@N alloy, the active medium in these optoelectronic devices. In the present work photoluminescence (PL), photoluminescence excitation (PLE) and Cathodoluminescence (CL) are used to investigate emission and absorption mechanisms in cubic 100 nm thick In@sub x@Ga@sub 1-x@N epitaxial layers grown on thick GaN/GaAs(001) buffer layers by MBE. High resolution x-ray diffraction (HRXRD) revealed that the InGaN layers were pseudomorphic with the GaN buffer. The In fraction x was calculated from the strained lattice constants obtained from the HRXRD reciprocal space maps. Reflectivity was used to measure the thickness of our films. PL and PLE spectra were recorded at 7 K and 300 K. CL spectra were performed at room temperature. The main features observed in the PL spectra are the characteristic emission from the band edge region of c-GaN and a lower energy peak which we ascribe to the InGaN layer. From the PLE spectra, we have determinated the alloy energy gap as a function of the In content. Comparing results from PL and PLE we observe a large Stokes-like shift for all samples. Another absortion band at lower energy than that of the alloy energy gap is observed on some of the PLE spectra. We tentatively ascribe this band to an absorption mechanism taking place in In-rich regions in the InGaN alloy. These findings are supported by a multi-peak structure obtained by PL and depth-resolved CL. In depht-resolved CL, the relative intensity of the peaks changes with increasing excitation depth, indicating a second InGaN fase close to the GaN/InGaN interface.