Cathodoluminescence depth-profiling studies of GaN/AlGaN quantum-well structures
- PDF / 262,381 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 229 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Cathodoluminescence depth-profiling studies of GaN/AlGaN quantum-well structures M. Godlewski Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Al. Lotniko´w 32/46, Poland
E.M. Goldys Semicond. Sci. & Technol. Lab., Macquarie University, North Ryde, 2109 NSW, Australia
M.R. Phillips Microstructural Analysis Unit, University of Technology, Sydney, Australia
R. Langer and A. Barski CEA-Grenoble, DRFMC/SP2M, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France (Received 24 July 1999; accepted 1 November 1999)
In this paper we evaluate the in-depth homogeneity of GaN epilayers and the influence of electric field present in strained GaN/AlGaN heterostructures and quantum wells on the yellow and “edge” emission in GaN and AlGaN. Our depth-profiling cathodoluminescence measurements show an increased accumulation of defects at the interface. Inhomogeneities in the doping level are reflected by the enhancement of the yellow emission in the interface region. The piezoelectric effect is found to strongly reduce the emission from the strained AlGaN quantum-well barriers. We also show that Ga droplets, commonly found on surfaces of samples grown in Ga-rich conditions, screen the internal electric field in a structure and thus result in a local enhancement of the edge emission intensity.
I. INTRODUCTION
II. EXPERIMENT
Despite a wide use of GaN-based structures in optoelectronics devices, several fundamental questions still remain unanswered. In particular, a relationship among morphology of layers, light emission, and effects related to piezoelectric fields in strained AlGaN/GaN heterostructures are not fully understood.1–4 The purpose of the present work is to examine these effects and their influence on the radiative recombination processes in GaN/ AlGaN heterostructures and quantum wells and to characterize the properties of such structures which depend on the location along the growth axis. We apply the technique of scanning electron microscopy (SEM) and scanning and depth-profiling cathodoluminescence (CL) to analyze the in-plane and in-depth properties of a series of three GaN/AlGaN heterostructures. Results of the CL depth-profiling of two GaN/AlGaN quantum-well (QW) structures are compared with those obtained on a GaN/ AlGaN heterostructure with relatively thick GaN and AlGaN layers, all grown by molecular beam epitaxy (MBE) at similar growth conditions. Effects of the piezoelectric field are discussed, and electric field-related modifications of the emission from GaN QWs are described. To the best of our knowledge this is the first use of the CL technique for the evaluation of effects of strong internal electric fields in GaN-based QW structures.
The CL and SEM images and the CL spectra were taken in a JEOL35C scanning electron microscope with a MonoCL2 CL system by Oxford Instruments, using a 1200 lines/mm grating blazed at 500 nm and detected using a Hamamatsu R943-02 Peltier cooled photomultiplier. The spectra were not corrected for system’s response.
Data Loading...
