Growth and characterization of ZnO thin films on GaN epilayers

Abstract

Dense ZnO(0001) films formed at 500°C via coalescence of islands grown via metalorganic vapor phase epitaxy (MOVPE) either on GaN/AlN/SiC(0001) substrates or on initial, coherent ZnO layers. Conical crystallites formed due to thermal expansion-induced stresses between the ZnO and the substrate. Interfaces between the ZnO films on GaN epilayers exposed either simultaneously to diethylzinc and oxygen or only to diethylzinc at the initiation of growth were sharp and epitaxial. Interfaces formed after the exposure of the GaN to O 2 were less coherent, though an interfacial oxide was not observed by cross-sectional transmission electron microscopy (TEM). Threading dislocations and stacking faults were observed in all films.

Growth of dense ZnO films via MOVPE on GaN(0001) epilayers using a low/high-temperature sequence

“…Microcracks were also observed in films exceeding the thickness of 600 nm (three iterations) due to residual stresses within the (0 0 0 1) planes caused primarily by the mismatch in the coefficients of thermal expansion between ZnO and GaN which produce in-plane tensile stresses in the ZnO on cooling and secondarily by any remaining mismatch in the lattice parameters between these two materials that has not been accommodated by misfit and threading dislocations, as reported in Ref. [28]. The results of triple-axis XRD measurements shown in Fig.…”

“…1 is believed to be primarily a result of strongly preferred growth along the [0 0 0 1] axis at this temperature. Previous X-ray photoelectron spectroscopy and/or atomic force microscopy studies in this laboratory by Smith et al [19] of the initiation of growth at 450 1C and 500 1C [28] of ZnO on similar GaN(0 0 0 1) films grown in the same reactor as the samples used in this research revealed that the former nucleated and grew in the Stranski-Krastanov mode, i.e., initially as a strained thin film and subsequently as separate, small, highly textured islands primarily on the terraces and secondarily at the steps of the latter. We argue that the needles observed in Fig.…”

A comprehensive review of ZnO materials and devices

“…Interfaces formed after the exposure of the GaN to O 2 were less coherent, though an interfacial oxide was not observed by cross-sectional TEM. 278 A strong effect of the surface polarity was revealed for homoepitaxial growth of ZnO films on O-and Znterminated ZnO ͑0001͒ substrates. 279 The films, grown on O-terminated ZnO surfaces were initially dense.…”

“…͑0001͒ films formed via coalescence of islands either on GaN / AlN / SiC ͑0001͒ substrates or on initial, coherent ZnO layers. 278 To check the possible effect of interface oxide layer on the growth mode and film morphology, the GaN surface was preexposed to the reagents in different ways at the initiation of growth. Interfaces between ZnO and GaN exposed either simultaneously to diethylzinc and oxygen or only to diethylzinc were sharp and epitaxial.…”

Optical and photoelectrical properties of ZnO thin films and the effects of annealing

“…films with low defect-density and therefore strong luminescence, is essential for the development of this new and exciting material for commercial use. A large number of studies on different ways of synthesising ZnO thin films has been carried out by many different groups, such as thermal oxidation [3,4], MOCVD [5,6], and MBE [7,8]. The goal is to fabricate the material with high resistivity, low carrier concentration and high mobility that allow efficient p-type doping to take place.…”