Electric Field Distribution in strained p-i-n GaN/InGaN multiple quantum well structures
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Internet Journal Nitride Semiconductor Research
Electric Field Distribution in strained p-i-n GaN/InGaN multiple quantum well structures. A. N. Cartwright1, Paul M. Sweeney1, Thomas Prunty1, David P. Bour2 and Michael Kneissl2 1Electrical 2Xerox
Engineering, State University of New York at Buffalo, Buffalo, NY 14260, Palo Alto Research Center,
(Received Thursday, August 26, 1999; accepted Wednesday, October 20, 1999)
The presence of piezoelectric fields within p-i-n GaN/InGaN multiple quantum well structures is discussed. Time integrated and time-resolved photoluminescence measurements and theoretical calculations of the effect of these fields is presented. Furthermore, a description of how these fields influence the carrier dynamics and a discussion of how the piezoelectric field effects the design of GaN/InGaN devices is presented.
1
Introduction
III-N materials continue to be the focus of research on the development of UV/blue semiconductor optoelectronics [1] [2]. This is predominantly due to the success of Nakamura et. al at Nichia to develop blue semiconductor laser sources with lifetimes sufficient for incorporation into consumer optoelectronics [3] [4] [5] [6] [7]. With all of the attention paid to device operation, relatively little attention has focused on the fundamental properties of these materials. However, recently much interest has focused on the presence of piezoelectric fields within the quantum wells of InxGa1-xN/GaN heterostructures [8] [9] [10] [11]. More importantly, much research has focused on how the presence of this field will affect the design of devices based on this material. It has been recently reported that these piezoelectric fields are quite large (between 300 to 800 kV/cm for 20 % Indium [10] [11]). This field is the direct result of the lattice mismatch between GaN and InN. The lattice constant of InGaN increases from that of GaN to the larger value of InN as the In content increases, resulting in compressive strain within the InGaN quantum well [11]. In addition, it has been shown that the piezoelectric electric field points toward the substrate for materials grown on a c-plane Sapphire substrate [11]. As we will demonstrate later, this is quite convenient for samples that are grown with n+ GaN deposited on this substrate. Specifically, this orientation allows the built-in electric field of the p-i-n structure, Ebi, to partially compensate for the induced piezoelectric field.
In this paper, we provide some basic theoretical calculations and continuous wave and time-resolved photoluminescence experiments to demonstrate the effects of the piezoelectric field. We present a systematic approach of studying three samples with specific structures to verify the presence of the piezoelectric field. Specifically, we use a technique, that has been used successfully in work on (111) materials [12] [13] [14], to calculate the electric field within the quantum well for piezoelectric materials embedded within a p-i-n structure. Furthermore, we demonstrate that these calculations, and s
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