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Carrier compensation traps in n−-GaN drift layers grown on Si substrates were investigated using high-temperature deep-level transient spectroscopy (DLTS). The upper limit of the temperature range (700 K) allows for the study of deeper levels in the bandgap than those previously reported by conventional DLTS. Three trap states were revealed to be responsible for carrier compensation. Besides the residual carbon (C) acceptor, two deep electron traps detected in the DLTS high-temperature range, labeled E2 and E3 with energies EC of 0.98 and 1.38 eV, respectively, were also found to have contributions to the carrier compensation. A comprehensive investigation combining with positron annihilation spectroscopy measurements revealed that E2 and E3 are related to the (–/2–) and (0/–) acceptor levels of the VGa–ON complex, respectively. The relatively high concentrations of E2 and E3 imply that the VGa–ON complex is an essential carrier compensation source in the drift layer and plays a crucial role in developing kV-class vertical GaN power devices.

We have investigated the growth of AlN films on hexagonal nano-concave-circle patterned Si substrates using metal–organic chemical vapor deposition. By depositing a thin AlN seed layer on the Si substrate before the pattern process, a high quality AlN film with a thickness of 2 μm has been obtained. The full width at half maximum values of X-ray diffraction rocking curves are as low as 409 and 677 arc sec for AlN (002) and (102) planes, respectively. Further experimental results indicate that the AlN seed layer can suppress the misorientation of the adjacent grains, as revealed by the lower twist and tilt angles of the mosaic structure, and thus only a few dislocations generated during the grain coalescence. In addition, the migration of Al adatoms is enhanced on the Al terminated surface of the AlN seed layer, which accelerates the coalescence process. All these improvements are attributed to the lower binding energy and diffusion barrier for Al adatoms on the Al terminated surface than that on the Si surface. Our results demonstrate an effective approach to obtain high quality AlN films for high performance ultraviolet light-emitting diodes on the Si substrate.

One of the challenges for GaN-on-Si radio frequency (RF) device applications is the RF loss, which is mainly associated with a parasitic channel formed at the interface of AlN and high-resistivity Si substrates. However, the type of conductivity and formation mechanism of the parasitic channel remains controversial. Here, we report unambiguous evidence of Al diffusion at the AlN/Si interface and its effect on RF loss. Hall measurements reveal p-type conductivity at the interface. By combining with secondary ion mass spectroscopy measurements, the p-type conductivity is attributed to the Al diffusion from the AlN layers into the Si substrates, with Al being an acceptor in Si. Experimental data and simulations are in good agreement. We also demonstrate that substrate nitridation can indeed promote the formation of an amorphous silicon nitride layer, which plays a role in suppressing the Al diffusion and, thus, reducing the RF loss.

Nanohole array is particularly advantageous for light field manipulation. Here, we report a strategy to mimic the function of x-ray transmission gratings with free-standing quasiperiodic nanohole array. An analytical description is developed to reveal the physical mechanism of the free-standing quasiperiodic nanohole array that reduces higher-order contamination, and is verified by rigorous numerical simulations. An x-ray free-standing quasiperiodic nanohole array consisting of 1.6 × 109 nanoholes over an active area of 10 mm × 10 mm was fabricated. Experimental results of near-complete suppression of higher-order diffractions were obtained in the x-ray region. The capability to separate multiple overlapping orders makes this kind of nanohole array attractive for future development and application of high-resolution spectroscopy.

We demonstrate a mid-infrared surface-emitting photonic crystal laser on silicon substrate operating at room temperature. The active region consisting of PbSe/PbSrSe multiple quantum wells was grown by molecular beam epitaxy on Si(111) substrate patterned with a photonic crystal (PC) array. The PC array forms a transverse magnetic polarized photonic bandgap at around 2840 cm−1. Under pulsed optical pumping, room temperature multimode lasing emissions were observed at wavelength ∼3.5 μm with estimated threshold peak pumping intensity of 24 kW/cm2. Angular-dependent measurement indicates the lasing is of a Gaussian-like profile with full width at half maximum of 4.66°.

We describe an IV-VI semiconductor light emitter consisting of a PbSe/PbSrSe multiple quantum well active region grown by molecular beam epitaxy on a patterned Si(111) substrate with a two dimensional (2D) photonic crystal (PC) array. The 2D PC array was designed to form photonic band gaps around 1960 and 2300 cm−1. Under pulsed optical pumping, light emission was observed with strongly coupled PC defect modes, which correspond well with simulated photonic band gaps. The observed spectral linewidth was around 10 cm−1 and the highest quantum efficiency measured was 12.8%.

The nonlinear photoinduced anisotropy with large birefringence in a bacteriorhodopsin/polymer composite (bR/PC) film was observed. The contrast ratio, a ratio of the maximum to the minimum intensity of transmitted probe light through the bR/PC film within the linear gray scale range could reach ∼350:1. An all-optical image display in different colors was performed. The intensity of the transmitted signal could be modulated by adjusting the multibeam polarization states and intensities. Therefore, the positive image, negative image, and image erasure in display were demonstrated.