We report the field emission properties of the quasi-aligned aluminum nitride (AlN) nanotips grown on differently doped ($p^{+}$ , $p$ , $n^{+}$ , and $n$ type) silicon (Si) substrates by thermal chemical vapor deposition. The AlN nanotips were $10\mathrm{nm}$ at the apex, $100\mathrm{nm}$ at the bottom, and $1200\mathrm{nm}$ in length. The AlN nanotips grown on $p^{+}\text{-}\mathrm{Si}$ substrate showed the lowest turn-on field of $6\mathrm{V}∕\mu \mathrm{m}$ (highest current density of $0.22\mathrm{A}∕{\mathrm{cm}}^2$ at a field of $10\mathrm{V}∕\mu \mathrm{m}$ ), whereas no significant emission could be obtained using $n^{+}$ - and $n\text{-}\mathrm{Si}$ substrates. Band diagrams of the Si–AlN heterojunction have been used to explain the phenomenon. A 5% variation of the applied field was observed while drawing a current density of $100\mu \mathrm{A}∕{\mathrm{cm}}^2$ from the nanotips grown on $p^{+}\text{-}\mathrm{Si}$ substrates.

The results of photoluminescence (PL), detection-energy-dependent photoluminescence excitation (DEDPLE), excitation-energy-dependent photoluminescence (EEDPL), and strain state analysis (SSA) of three InGaN/GaN quantum-well (QW) samples with silicon doping in the well, barrier and an undoped structure are compared. The SSA images show strongly clustering nanostructures in the barrier-doped sample and relatively weaker composition fluctuations in the undoped and well-doped samples. Differences in silicon doping between the samples give rise to the differences in DEDPLE and EEDPL spectra, as a result of the differences in carrier localization. In addition, the PL results provide us clues for speculating that the S-shaped PL peak position behavior is dominated by the quantum-confined Stark effect in an undoped InGaN/GaN QW structure.