Ultraviolet light emitting diodes using non-polar A-plane AlGaN multiple quantum wells
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Ultraviolet light emitting diodes using non-polar A-plane AlGaN multiple quantum wells Ramya Chandrasekaran, Anirban Bhattacharyya, Ryan France, Christos Thomidis, Adrian Williams, and Theodore Moustakas Electrical Engineering, Boston University, Boston, MA, 02215 ABSTRACT In this paper, we report the growth and fabrication of non-polar A-plane AlGaN multiple quantum well based ultraviolet light emitting diodes (UV-LEDs). The LEDs were grown on R-plane sapphire substrates using molecular beam epitaxy (MBE). The Currentvoltage characteristics of the fabricated devices demonstrated rectifying behavior with a series resistance of 38 ohms. An electro-luminescence emission at 338 nm was obtained. INTRODUCTION GaN and its alloys have attracted extensive attention for their applications in UV-blue emitters, solar blind photo detectors and transistors for high power and high temperature applications. The majority of the work reported in the literature was done on films and devices grown along the polar direction [0001] or [000 1 ]. However, conventional (0001) C-plane multiple quantum well (MQW) based LEDs suffer from the quantum confined Stark effect (QCSE) due to the presence of the spontaneous and piezoelectric polarization vectors along the [0001] or [000 1 ] directions. While such an effect may be useful in some devices, such as optical modulators, field effect transistors etc., they are undesirable in other devices such as emitters. Generally, III-nitride UV emitters based on AlGaN MQWs grown along the [0001] direction are designed to have thin quantum wells in order to mitigate the problems associated with the QCSE. An alternative approach of addressing the issue of polarization-induced internal electric field is by growing wurzite group III-nitride MQW-based LEDs along the non-polar directions. Recently, there has been significant attention on the growth of GaN and related MQWs along non-polar directions. There are several experimental reports indicating the absence of QCSE on the MQWs grown along the non-polar directions [1-3]. However, there are very few reports on the development of LEDs along the non-polar directions. Chitnis et al. and Chakraborty et al. have reported the development of visible LEDs using InGaN/GaN MQWs along the [11 2 0] and [1 1 00] directions respectively [4,5]. Chen et al. reported the development of UV-LED emitting at 363 nm using GaN/AlGaN MQWs grown along the [11 2 0] direction [6]. In this paper, we report A-plane UV-LED emitting in the wavelength region of 330-340 nm, grown on R-plane sapphire substrate using molecular beam epitaxy. EXPERIMENTAL METHODS A-plane (11 2 0) III-nitrides were grown by RF plasma-assisted molecular beam epitaxy (PAMBE) in a Varian Gen-II system using the Applied Epi RF plasma source to activate the molecular nitrogen. Ga and Al were supplied from Applied Epi SUMOTM effusion
cells; Mg and Si were supplied from standard effusion cells. The fabricated devices were tested on a wafer level and all the measurements were carried out at room temperatur
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