Effect of HVPE GaN Substrate Condition on the Characteristics and Performance of 405 nm LEDs
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0916-DD05-02
Effect of HVPE GaN Substrate Condition on the Characteristics and Performance of 405 nm LEDs James R Grandusky1, Muhammad Jamil1, Vibhu Jindal1, Fatemeh Shahedipour-Sandvik1, Hai Lu2, Xian-An Cao2, and Edmund B Kaminsky2 1 College of Nanoscale Science and Engineering, University at Albany, Albany, NY, 12203 2 General Electric Global Research Center, Niskayuna, NY, 12309 ABSTRACT This article reports on the effects of HVPE GaN substrate condition on the performance of 405 nm LEDs grown by MOCVD. Three 1 cm2 HVPE GaN substrates were received from a commercially available source and characterized for the substrate condition. AFM and optical microscope were used to characterize the surface morphology and this was found to vary from a “moonscaped” morphology to a smooth surface. The presence of nanoscale pits and substrate bowing were also found. XRD measurements showed a variation in crystalline quality of the substrates with the FWHM of the (0002) rocking curve varying from 87 arcsec to 192 arcsec with some substrates showing multiple peaks in the rocking curve. Photoluminescence was used to measure the optical quality of the substrates and both band edge luminescence and yellow luminescence were found to vary greatly within one substrate as well as from substrate to substrate. After characterization of each individual substrate a 405 nm LED structure was grown using identical growth conditions on each substrate, in separate growth runs. A GaN template was included in each growth for consistency. The surface morphology and crystalline quality of the device structures were then measured. Following this devices were fabricated and tested for electroluminescence optical output power and current-voltage characteristics. The device characteristics and performance as related to starting substrate quality will be presented with respect to substrate surface morphology and crystalline structure. INTRODUCTION The introduction of low dislocation density free standing HVPE GaN substrates has led to many reports on the advantages of such substrates in the growth of optoelectronic devices such as Light Emitting Diodes (LED) [1,2] and Laser Diodes (LD) [3]. Due to the high cost and limited availability there are no reports on the optimization of growth conditions on these substrates relative to typical growth on sapphire substrates. However as this is a new technology and it is continuously being improved, it is first necessary to study the substrates themselves and the variability in the quality of the substrates. Even more important is the effect of the starting substrate properties on the performances of devices grown and fabricated on these substrates. Little optimization can be completed if the growth depends heavily on the substrate condition. In order to measure the effect of starting substrate condition on device performance, three substrates with the same specifications were purchased from a commercially available source. A 405 nm LED device structure was grown on each sample in separate growth runs. A GaN temp
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