Nonpolar Light-emitting Diodes

In 2003, Chen et al. reported 363-nm ultraviolet LED using nonpolar a-plane AlGaN/GaN MQWs [25]. In 2004, Chitnis etol. reported visible LED using nonpolar a-plane InGaN/GaN MQWs [26]. Till 2004, there were no reports on optical power performance of nonpolar light emitters. The lack of low-defect density templates or substrates for the growth of LEDs was probably 

The purpose of this section of the chapter is to describe the growth, structural, electrical, and optical properties of nonpolar a-plane and m-plane LEDs using InGaN/GaN MQW structures grown by MOGVD. 

In this section, fabrication and electrical and luminescence characteristics of nonpolar a-plane violet, blue, and cyan InGaN/GaN LEDs using reduced-defect LEO a-plane GaN template have been discussed. In particular, the effect of drive current on output power, emission wavelength, and linewidth in the electroluminescence (EL) emission spectra were investigated. The current-voltage I-V) characteristics of the diodes have also been studied. 

Cross-sectional transmission electron microscope with an FEI Tecnai G2 Sphera microscope operating at 200 kV was used to image the MQW microstructure. The as-grown samples were investigated by PL measurements. 

300 X 300 im diode mesas were defined by chlorine-based reactive ion etching (RIE). Pd/Au (3/200 nm) and Al/Au (30/200 nm) were used as fi-GaN and n-GaN contacts, respectively. The electrical and luminescence characteristics of the diode were measured by on-wafer probing of the devices. The I-V measurements were performed with a Hewlett-Packard 4155B semiconductor parameter analyzer. Relative optical power measurements under direct current (DC) conditions were obtained from the backside emission through the sapphire substrate onto a calibrated broad area Si photodiode. The emission spectrum and the optical power emission of the LEDs were measured as a function of drive currents. All measurements were carried out at room temperature. 

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