Growth and Properties of AlGaInP Resonant Cavity Light Emitting Diodes (RCLEDs) on Ge/SiGe/Si Substrates
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Growth and Properties of AlGaInP Resonant Cavity Light Emitting Diodes (RCLEDs) on Ge/SiGe/Si Substrates O. Kwon1, J. Boeckl1, M. L. Lee2, A. J. Pitera2, E. A. Fitzgerald2, and S. A. Ringel1 The Ohio State University, Department of Electrical Engineering, 2015 Neil Avenue Columbus, OH 43210, U.S.A. 2 Massachusetts Institute of Technology, Department of Materials Science and Engineering, 77 Massachusetts Avenue Cambridge, MA 02139, U.S.A. 1
ABSTRACT AlGaInP visible resonant cavity light emitting diodes (RCLEDs) were grown and fabricated on low-dislocation density, SiGe/Si metamorphic substrates by molecular beam epitaxy. A comparison with devices grown on GaAs and Ge substrates showed that not only did the RCLED device structure successfully transfer to the SiGe substrate, but also a higher optical output power was obtained. This is a result of a high thermal conductivity and an enhanced lateral current spreading. In addition, the growth of an AlGaAs current spreading layer and a modified top metal contact were incorporated to the SiGe RCLED to improve the device performance. With these improvements, a 410µm × 410µm device was fabricated with an optical power of 166µW at 665nm peak wavelength under 500mA current injection and an extremely narrow full width half maximum (FWHM) value of 3.63nm for electroluminescent emission under 50mA injection current. INTRODUCTION III-V optoelectronic integration on silicon integrated circuits is of great interest due to the potential of increasing the functionality of Si integrated circuits and to the possibility of integrating high speed optical interconnects within VLSI circuitry [1]. Historically, the monolithic integration of III-V compounds with Si has been challenged by fundamental mismatches in lattice constant, thermal expansion coefficient and crystal structure. Recent work on graded SiGe relaxed buffers, however, has created a new opportunity for success with the demonstration of low threading dislocation density (~ 1×106 cm-2) achieved for relaxed Ge over large area of Si wafers. Moreover, use of these substrates has led to the demonstration of devicequality GaAs growth resulting in high-performance GaAs/Si solar cells and GaAs/AlGaAs based laser diodes [2-4]. Continuing this theme, this paper explores the integration of phosphorous (P) based visible (650nm) AlGaInP resonant cavity light emitting diodes (RCLED) grown on relaxed Ge/SiGe/Si substrates, using solid source molecular beam epitaxy (MBE). EXPERIMENTAL DETAILS III-V device layers were grown on compositionally step-graded SiGe/Si substrates where the SiGe buffer is graded from Si to Ge at an average grading rate of 10% Ge/µm. Details of the SiGe step graded buffer growth on offcut (001) Si by ultra high vacuum chemical vapor deposition (UHVCVD) can be found in previous work [5]. The threading dislocation density
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(TDD) in the topmost relaxed Ge layer of the buffers is ~1×106 cm-2 as determined by both plan view transmission electron microscope (TEM) and etch pit density measurements (EPD). The S
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