Structural And Optical Properties Of Nonpolar M- And A-Plane Gan/Algan Heterostructures For Narrow-Linewidth Mid-Infrared Intersubband Transitions

Mid-infrared intersubband transitions are investigated in nonpolar m-plane and a-plane GaN/AlGaN multi-quantum well heterostructures. Nominally identical heterostructures were grown by ammonia molecular-beam epitaxy on free-standing m-plane and a-plane GaN substrates. A total of 12 well- and barrier-doped samples with intersubband transition energies in the range of 220-320meV (wavelength range 3.8-5.6 mu m) were grown. The intersubband absorption lines of the m-plane samples were 10-40% narrower than those of the a-plane samples, and a very narrow intersubband absorption linewidth of 38meV (full width at half maximum) at a transition energy of approximately 250meV (5 mu m wavelength) was observed in an m-plane sample. Narrower intersubband absorption linewidths of m-plane samples can be explained by more abrupt heterostructure interfaces revealed by structural characterization, which is attributed to a higher stability of the m-plane compared to the a-plane. No significant difference in the intersubband absorption linewidth was observed between the barrier- and well-doped samples.