Study of Optical Gain in Thick GaN Epilayers by Variable Stripe Length Technique
- PDF / 161,605 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 2 Downloads / 157 Views
V4.4.1/FF4.4.1
Study of Optical Gain in Thick GaN Epilayers by Variable Stripe Length Technique G. Tamulaitis1, J. Mickevičius2, M. Shur2, Q. Fareed3, and R. Gaska3 Institute of Materials Science and Applied Research, Vilnius University, Saulėtekio 9-III, LT-10222 Vilnius, Lithuania 2 Department of ECE and CIE, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. 3 Sensor Electronic Technology, Inc., 1195 Atlas Road, Columbia SC 29209, U.S.A. 1
ABSTRACT We report on the gain study in high-quality thick GaN layers using the Variable Stripe Length (VSL) technique. The layers were grown by Migration Enhanced Metal Organic Chemical Vapor Deposition (MEMOCVDTM). The amplification of light was investigated for the propagation directions along the layer surface (perpendicular to the c-axis of the crystal) and perpendicular to the layer (along the c-axis) for the layers with thicknesses up to 11 µm. By fitting the experimental stripe length dependence of the edge luminescence with one-dimensional description of light amplification in medium with positive gain, peak gain coefficients of up to 7300 cm-1 were estimated in GaN at the excitation power density of 2 MW/cm2. We discuss limitations of the VSL technique due to the assumption of one-dimensional light propagation and strong influence of gain saturation in a high-gain medium. The contribution of new gain modes after saturation of the highest-gain modes was observed. The optical gains in GaN samples with different carrier lifetimes (obtained using time-resolved photoluminescence and light-induced transient grating techniques) were compared. INTRODUCTION III-nitrides and their heterostructures have found applications for green, blue, and ultraviolet light emitters. However, in spite of commercialization of blue and UV light emitting diodes, development of III-nitride-based laser diodes (LDs) is succesful only for LDs with InGaN active layers. Meanwhile, theoretical estimates [1] predict high optical gain values of up to 25 000 cm-1 in GaN, since this semiconductor with the room-temperature band gap of 3.42 eV corresponding to the peak emission wavelength of 362 nm has a high joint density of states due to high effective electron mass and close overlap of three valence subbands near the band gap. Experimental gain values of up to 2700 cm-1 in heteroepitaxial GaN [2] and 7200 cm-1 in homoepitaxial GaN [3] have already been reported. However, measurements of such high gain values encounter some problems. The most straightforward way to measure the gain coefficient is the excite-and-probe technique [4]. Unfortunately, difficulties in preparation of a transparent sample thin enough for such measurement (usually thinner than 1 µm) often make this technique unattractive or even unacceptable. In structures with laser cavities, a method based on the study of Fabry-Perot longitudinal modes (the Hakki-Paoli technique [5]) is usually employed. However, perhaps the most common method to estimate the optical gain in semiconductors in general and in GaN in particular [2,3,6] is th
Data Loading...
