In-depth and in-plane profiling of light emission properties from semiconductor-based heterostructures M. GODLEWSKI *1,2 , T. WOJTOWICZ 1 , E.M. GOLDYS 3 , M.R. PHILLIPS 4 , R. CZERNECKI 5 , P. PRYSTAWKO 5 , M. LESZCZYNSKI 5 , P. PERLIN 5 , I. GRZEGORY 5 , S. POROWSKI 5 , T. BÖTTCHER 6 , S. FIGGE 6 , and D. HOMMEL 6 1 Institute of Physics, Polish Acad. Sci., 32/46 Lotników Ave., 02-668 Warsaw, Poland 2 Department of Mathematics and Natural Sciences College of Science, Cardinal S. Wyszyñski University, 5 Dewajtis Str., 01-815 Warsaw, Poland 3 Division of Information and Communication Sciences, Macquarie University, Balaclava Road, NSW Sydney 2109, Australia 4 Microstructural Analysis Unit, University of Technology, PO Box 123, Broadway NSW Sydney 2007, Australia 5 High Pressure Res. Centre (Unipress), Polish Acad. Sci., 29/37 Soko³owska Str., 01-142 Warsaw, Poland 6 Institute of Solid State Physics, University of Bremen, D-28334 Bremen, Germany Cathodoluminescence (CL) technique is applied for evaluation of in-depth and in-plane variations of light emission from semiconductor heterostructures, including laser diode structures. Light emission properties of heteroepitaxial and homoepitaxial structures are studied. We demonstrate possibility of in-depth profiling of complicated multi quantum well structures, which allows us to evaluate light emission characteristics from different regions of, e.g., laser structures. Due to this property of the CL, we can evaluate interconnections between structural quality of the samples and light emission char- acteristics. Stimulated emission under electron beam pumping is achieved in a conventional CL set up for selected heterostructures. Threshold currents for stimulated emission are evaluated from the CLinvestigations. We demonstrate that potential fluctuations are not fully screened in the active regions of laser structures, even at large excitation densities. Keywords: semiconductors, heterostructures, cathodoluminescence, depth-profiling, defect distribution, laser emission. 1. Introduction A wide spread use of semiconductor materials in electronic and opto-electronic devices promotes detail studies of their properties. Most of available experimental techniques aver- ages material properties, making difficult to conclude on in-plane and in-depth distribution of defects and impurities. In this work, we demonstrate that such information can be obtained from scanning, spot-mode and in depth-profiling cathodoluminescence (CL) investigations. We show that in-plane and in-depth properties of semiconductor quantum well (QW) heterostructures can be studied with atomic-like resolution, which enables direct observation of light emis- sion from active regions of semiconductor-based devices, as demonstrated for GaN-based laser diode (LD) structure. 2. Experimental The CL spectra were taken in a JEOL35C scanning elec- tron 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. Spectra were not corrected for the system’s response. The electron beam current I b was mea- sured using a Faraday cup. All spectra discussed here were taken at room temperature. Charging effects were carefully minimized. 3. Basics of CL depth-profiling experiments Resolution of CL investigations is not that of focused beam of primary electrons, but depends on a radius of a scattered cloud of primary and secondary electrons and on a diffu- sion length of carriers or excitons [1–3]. Information on in-plane emission properties, obtained by scanning electron beam through a given area, is thus limited to at least 50 to 100 nm [3]. In-depth resolution is available through CL in- vestigations taken with varying beam energy (accelerating voltage) [1,2,4–7]. Interpretation of the depth profiling CL data is based on a theory of CL depth-profiling experiments shortly described below. Empirical function describing Opto-Electron. Rev., 12, no. 4, 2004 M. Godlewski 353 Invited paper 4 th International Conference on Solid State Crystals OPTO-ELECTRONICS REVIEW 12(4), 353–359 * e-mail: godlew@ifpan.edu.pl