Strong ultraviolet emission from non-polar AlGaN/GaN quantum wells grown overr-plane sapphire substrates

Abstract

GaN and GaN/Al0.25Ga0.75N multiple quantum wells (MQWs) over c‐ and r‐plane sapphire substrates have been grown by metal‐organic chemical vapor deposition. A comparative study of photoluminescence (PL) in GaN epitaxial layers and AlGaN/GaN MQWs on these two types of substrates is reported. At low excitation levels, the measured room temperature PL signal in GaN layers grown over r‐plane sapphire was more than order of magnitude lower than in GaN on c‐plane substrates. In contrast, the emission intensity from AlGaN/GaN MQWs grown over r‐plane substrates was almost 30 times stronger than in the structures grown over c‐plane sapphire. Furthermore, with excitation power density up to 1 MW/cm2, the PL peak position for the non‐polar MQWs kept completely stable whereas the one for the c‐plane structures exhibited a blue shift as large as 250 meV. We attribute this large difference in the ultraviolet emission intensity to the suppression of a strong quantum Stark effect in the AlGaN/GaN MQWs on the r‐plane sapphire. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of initial stages on the crystal quality of nonpolar a-plane AlN on r-plane sapphire by low-pressure HVPE

“…However, the quantum efficiency (QE) of deep-UV LEDs is presently very low in comparison with that of blue LEDs. Two factors, the poor quality of AlN or Al x Ga 1Àx N (x40.4), due to the large lattice-mismatch and the strong built-in electric field, due to spontaneous and piezoelectric polarization in the c-[0 0 0 1] direction, are attributed to the degradation of efficiency [2]. Fortunately, bulk nonpolar or semipolar AlN is a promising homo-substrate that can be employed to simultaneously overcome the two above-mentioned problems.…”

Characterization of optical properties and thermo-optic effect for non-polar AlGaN thin films using spectroscopic ellipsometry

“…Therefore, the quantum efficiency and the optical output power of the polar AlGaN-based deep UV-LED (DUV-LED) with higher Al composition are much lower than those of the blue LED with lower Al composition. Needless to say, the growth of the GaN-based semiconductors and related AlGaN alloys along non-polar direction is one of the most direct and effective ways for removing the negative influence of the QCSE [6][7][8]. However, the material growth and device fabrication for the non-polar AlGaN are still in quite preliminary stages.…”

Comparative study of n-type AlGaN grown on sapphire by using a superlattice layer and a low-temperature AlN interlayer

“…The strain depends on the crystal orientation [2], the thickness, and the chemical composition of the epitaxial layers [3]. Strain engineering [4] can be accomplished by superlattice (SL) layers [5], low-temperature (LT) AlN interlayers [6], homoepitaxial substrates [7,8], and non-polar substrates [9][10][11][12]. Among these approaches, AlGaN/AlGaN SLs and LT AlN interlayers are frequently used on (0 0 0 1)-oriented sapphire substrates.…”