Establishment of an Angle Resolved Reflectometry Setup to Characterize GaN LED Structure

Abstract

High quality, epitaxially grown GaN light emitting diode (LED) structure using metal organic vapor phase epitaxy (MOVPE) system is experimented in this report. A single and thin InGaN quantum well (QW) with the emission peak at the wavelength of 475 nm is grown epitaxially into this heterostructure as the active region. Next, a silver grating is formed on the heterostructure by electron beam lithography (EBL) and lift-off technique. Afterwards, the fabricated device is characterized with photoluminescence (PL), atomic force microscopy (AFM) and scanning electron microscopy (SEM) to examine the device quality.

An angle resolved optical setup is designed and built based on Fourier optics. For reflectometry operation, white light is incident on the sample at the grating side. The reflected light forms a Fourier plane after passing through an objective lens. This plane contains various reflection angles at different vertical positions. Then it is focused at a monochromator entrance slit by using a Fourier lens. The monochromator grating diffracts this Fourier image and finally angle vs. wavelength information is captured by a charge coupled device (CCD) camera, attached to the monochromator exit slit.

The CCD image exhibits Fabry-Perot interference arcs with no surface plasmon (SP) effect. This obtained data is then compared to the MATLAB simulated interference arcs by superimposing on them. Finally, the principle behind these obtained arcs are analyzed qualitatively to justify the instrumental performance.