Quantum band engineering of nitride semiconductors for infrared lasers

The III-nitride semiconductors have been proposed as candidate materials for new quantum cascade lasers in the near-infrared (1.5-3 mu m), and far-infrared (30-60 m), due to the large conduction-band offset between GaN and Al-containing alloys (>1 eV), and the large longitudinal optical (LO) phonon energy (90 meV), respectively. The challenges of III-nitride intersubband devices are twofold: material and design related. Due to large electron effective mass, the nitride intersubband materials require the ability to fine-tune the atomic structure at an unprecedented sub-nanometer level. Moreover, the III-N materials exhibit built-in polarization fields that complicate the design of intersubband lasers. This paper presents recent results on c-plane nitride resonant-tunneling diodes that are important for the prospects of far-infrared nitride lasers. We also report near-infrared absorption and photocurrent measurements in nonpolar (m-plane) AlGaN/GaN superlattices.