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Shortwavelength intersubband transitions in GaN/AlN superlattices

Figure 2. HRXRD experimental data on Ga-rich (blue) and N-rich (black) grown GaN/AlN superlattices with MadMax simulation (red). A thin layer of narrow band gap material sandwiched between two wide band gap material layers is called quantum well, which gives rise to one-dimensional carrier confinement. Due to the confinement of electrons within the conduction band, quasi-two-dimensional electronic states, or subband, are formed. The transitions between quantized energy levels are called intersubband transitions. The repetition of the quantum well is called superlattice. GaN/AlN superlattices (SLs) are very promising for developing visible to near infrared (IR) intersubband (ISB) devices due to the large conduction band offset (~2eV) and ultrafast scattering rate. Thus GaN/AlN (SLs) are extremely interesting for optical communication wavelength (1.3/1.55 ┬Ám) applications. This project focuses on plasma-assisted molecular beam epitaxial growth of superlattices, and the exploration of growth kinetic effect on structural properties and thus intersubband transitions. One of the unique properties of GaN/AlN system is the presence of the internal electric field at the interface of the heterostructure. The strong electric field appears as the result of polarization induced by the noncentro-symmetric property along c-axis in wurtzite-nitride. To circumvent deleterious electric field, non-polar orientation superlattices approach are under development.

Figure 1. Optical set-up and incident geometry of Intersubband (ISB) transition measurement. The sample is polished as a zigzag multipass waveguide with p-polarized light normal incident to one of two polished 45o edges (dotted yellow box). The polar (top) and non-polar (bottom) quantum-well band diagrams and ISB transitions are shown (dotted blue box).

Work sponsered by the Office of Naval Research (ONR)