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

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 /spl Aring/ 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 /spl mu/m depending on the well thickness and barrier height. This is the first observation of intersubband absorption at a wavelength as short as 1.5 /spl mu/m for the III-nitrides material system.