Intersubband absorption at λ ∼ 2.1 μm in A-plane GaN/AlN multiple quantum wells

Intersubband optical absorption at λ ∼ 2.1 μm wavelength in doped 17.5 Å wide GaN quantum wells (QWs) with 51 Å wide intermediate AlN barriers is reported. A ∼600 nm thick GaN template and 15 QWs have been grown by molecular beam epitaxy on R-plane sapphire substrate and display pure A-plane orientation. QWs with A-plane orientation are essentially free from spontaneous polarisation, which is expected to greatly simplify the design of GaN/Al(Ga)N devices employing intersubband transitions.