We report the deposition of a-Si:H on thin films of free-standing single crystalline ZnO columns. The ZnO columns have a height of several μm and a diameter between 100 and 200 nm. The ZnO films are prepared in electrodeposition and have considerable potential for use in photoelectric thin film devices. Morphology, electronic parameters, and basic optical behavior, such as reflectance and light trapping efficiency, are reported. Amorphous silicon is deposited on the columns as a continuous smooth film with conformal coverage. Some possibilities of using these films in devices are discussed.

Thick, entirely crack-free GaN-based light-emitting diode structures on 2 in. Si(111) substrates were grown by metalorganic chemical-vapor deposition. The ∼2.8-μm-thick diode structure was grown using a low-temperature AlN:Si seed layer and two low-temperature AlN:Si interlayers for stress reduction. In current–voltage measurements, low turn-on voltages and a series resistance of 55 Ω were observed for a vertically contacted diode. By in situ insertion of a SixNy mask, the luminescence intensity is significantly enhanced. A light output power of 152 μW at a current of 20 mA and a wavelength of 455 nm is achieved.

No abstract

GaN growth on heterosubstrates usually leads to an initially high dislocation density at the substrate/seed layer interface. Due to the initial growth from small crystallites, tensile stress is generated at the coalescence boundaries during GaN growth. In addition, with tensile thermal stress this leads to cracking of GaN on Si and SiC substrates when cooling to room temperature. By partially masking the typically applied AlN seed layer on Si(111) with an in situ deposited SiN mask a reduction in tensile stress can be achieved for the subsequently grown GaN layer. Additionally, the 6 K GaN band edge photoluminescence is increased by about an order of magnitude and shifts by 21 meV, which can be attributed to a change in tensile stress of ∼0.8 GPa, in good agreement with x-ray diffractometry measurements. This improvement in material properties can be attributed to a reduction of grain boundaries by the growth of larger sized crystallites and lateral overgrowth of less defective GaN.

GaN growth on Si is very attractive for low-cost optoelectronics and high-frequency, high-power electronics. It also opens a route towards an integration with Si electronics. Early attempts to grow GaN on Si suffered from large lattice and thermal mismatch and the strong chemical reactivity of Ga and Si at elevated temperatures. The latter problem can be easily solved using gallium-free seed layers as nitrided AlAs and AlN. The key problem for device structure growth on Si is the thermal mismatch leading to cracks for layer thicknesses above 1 µm. Meanwhile, several concepts for strain engineering exist as patterning, Al(Ga)N/GaN superlattices, and low-temperature (LT) AlN interlayers which enable the growth of device-relevant GaN thicknesses. The high dislocation density in the heteropitaxial films can be reduced by several methods which are based on lateral epitaxial overgrowth using ex-situ masking or patterning and by in-situ methods as masking with monolayer thick SiN. With the latter method in combination with strain engineering by LT-AlN interlayers dislocation densities around 109 cm -2 can be achieved for 2.5 µm thick device structures.