The bandgap energy versus lattice constant of the AlGaInN material system is shown in Fig. 13.2. The AlGaInN material system spans a very wide range of wavelengths covering the deep UV, near UV, visible, and even the near infrared spectral range. Of the three binary semiconductors InN, GaN, and AlN, epitaxially grown GaN has been shown to be synthesizable with the highest quality. It has generally been difficult to synthesize Al-rich AlGaN alloys and In-rich GaInN alloys with high internal quantum efficiencies.

There has been some controversy with respect to the bandgap energy of InN, which originally had been found to be about 1.9 eV. More recently, the bandgap energy was found to be much lower, namely 0.77 eV.

The energy-gap bowing can be expressed in terms of a constant, a linear term (<x x) and a non-linear term [ <x x (1 - x) ] according to

eAAB = EA + (EgB - EAA) x + x (1 - x) Eb (13.1)

with Eb called the bowing energy or bowing parameter. The bowing parameters used in Fig. 13.2 for AlGaN, GaInN, and AlInN are based on data published by Siozade et al. (2000), Yun et al. (2002), and Wu et al. (2002; 2003). Recently additional data on the bowing energies have become available (Walukiewicz et al., 2004).