GaN-based solid state lighting

Abstract

Summary form only given. Charge separation due to spontaneous and piezoelectric polarization inherent to the wurtzite structure has deleterious effects on the performance of most c-axis oriented devices. To overcome this problem, Nonpolar GaN, such as a-plain and m-plain GaN or semipolar GaN substrates have been grown. We reported the fabrication of violet InGaN/GaN Light Emitting Diodes (LEDs) on the first nonpolar m-plane (11macr00) GaN bulk substrates. The output power and External Quantum Efficiency (EQE) at a driving current of 20 mA were 28 mW and 45% respectively, with peak electroluminescence (EL) emission wavelength at 400 nm. The first nonpolar m-plane (11macr00) nitride laser diodes (LDs) were realized on low extended defect bulk m-plane GaN substrates. Broad area violet lasers were fabricated and tested under pulsed and CW conditions. These laser diodes had threshold current densities (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) as low as 2.3 KA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for pulsed and 7.5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for CW operation. Stimulated emission was observed around 405nm. Also, we fabricated high-efficient violet, blue, green and yellow LEDs, and violet laser diodes on semipolar GaN bulk substrates. The current biggest problem of nonpolar and semipolar devices is a limitation of the size of the GaN substrate. In order to make a real GaN bulk crystal, we have developed the ammonothermal method. Recently, we obtained the size of 6-8 mm bulk GaN crystal. The recent performance of nonpolar, semipolar and polar (c-plain) GaN-based devices, and bulk GaN growth are described.