Molecular beam epitaxy of GaN/AlGaN multiple quantum wells: Application to near-infrared intersubband transitions (1.5-4.2 μm)

High quality GaN/AlGaN multiple quantum wells were grown by molecular beam epitaxy on (0001) sapphire substrates. The GaN wells range in thickness between 10 and 30 Å while the AlGaN composition of the barriers was varied between 45 and 85%. Structural studies by cross-sectional transmission electron microscopy show that the GaN/AlGaN interfaces are abrupt with thickness uniformity on the order of one (Al)GaN monolayer. Intersubband absorption was observed between 1.5 to 4.2 μm depending on the well thickness and barrier height. This is the first observation of intersubband absorption at a wavelength as short as 1.5 μm for the III-nitrides material system