| In this thesis, three primary findings are presented concerning optolelectronic properties of AlGaN superlattices. First, we obtain the lowest lateral p-type resistivity and highest lateral p-type mobility to date in the AlGaN material system. Second, we obtain the first experimental results of multi-subband photoluminescence in p-type AlGaN superlattices. Last, we report the first direct measurement of per-pendicular electrical transport (electrical transport perpendicular to the superlattice planes) in AlGaN superlattices.; Our research into resistivity and mobility of AlGaN superlattices stems from the fact that p-type AlGaN is highly resistive. To overcome the problem of highly resistive p-type AlGaN, we propose and demonstrate modulation doping in p-tyr AlGaN superlattices. Our measurements yield a low-temperature lateral resistivity and mobility of 0.068 Ω · cm and 36 cm2/(V · s), respectively. This is the lowest resistivity and highest mobility recorded to date in p-type AlGaN and results from reduced ionized impurity scattering inherent in modulation doping.; The optical properties of AlGaN superlattices are of great interest because they are often used in light-emitting diodes and laser diodes. Specifically, the absorption edge in AlGaN superlattices is typically thought of as being severely red-shifted due to internal electric fields present in AlGaN-based materials. We obtain experimental photoluminescence results on large-period superlattices that indicate that the red-shifting of the absorption edge is much less than previously thought due to the combined effects of band-filling and oscillator strength on energy. We develop a computer model based on the self-consistent solution of the Poisson and Schrödinger system of equations. Our model predicts a drastic decrease in spontaneous recombination lifetime with increased transition energy, which is consistent with our experimental data.; The perpendicular resistivity of AlGaN superlattices is also of critical importance to the development of AlGaN-based devices. We therefore measured the perpendicular resistivity of an n-type AlGaN superlattice and compared it to bulk n-type GaN. The superlattice has a perpendicular resistivity of 1.2 Ω · cm while bulk n-type GaN is 0.18 Ω · cm. We develop a theoretical model based on sequential tunneling and enhanced free carrier concentration to explain our experimental findings. Our model shows that perpendicular resistivity is dominated by two factors; carrier concentration and tunneling probability. |
