Growth of ZnO(0 0 2) and ZnO(1 0 0) films on GaAs substrates by MOCVD
Introduction
ZnO is a wide band gap semiconductor. Currently, the application of ZnO is increases gradually. With the development of more and more superior thin film growth technology, the quantity has been improved greatly. Because of its special material characteristic (exciton binding energy ∼60 meV), ZnO as a kind of optoelectronic material has great application potential and draws attentions from many people. Strong exciton binding energy makes ZnO a promising material for the realization of efficient excitonic lasing at room temperature. Because of its strong exciton binding energy, ZnO film has been extensively studied considering their potential application in optoeletronics and photonic devices in the ultraviolet (UV) region [1], [2], [3], [4].
A stable p-ZnO film of high quantity is still hard to acquire, therefore there still remains lots of difficulties in the application study of the optoelectronic device. Many scientists have extensively carried out works using different methods (codoping, impurity doping and annealing, self diffusion of impurity) in order to obtain stable and high quantity ZnO film. At the same time, some scientists fabricate p–n heterojunctions using other semiconductor materials on ZnO film, to realize electron luminescence and carry on further research. The materials used for heterojunctions formation are commonly III–V group compound semiconductor (GaN, GaAs, InP, InSb, etc.) [5], [6], [7]. ZnO films grown on GaAs substrates have the possibility of p–n heterojunctons formation. GaAs substrates can provide As atoms which act as a p-type dopant and diffuse into the films. ZnO/GaAs films have been deposited using different techniques such as sputtering, molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) [8], [9], [10], [11], [12]. So far, there have been few reports on ZnO/GaAs films grown by metal-organic chemical vapor deposition (MOCVD).
This paper reports on characteristics of ZnO films grown on GaAs substrates by MOCVD under different growth temperatures and surface treatment conditions. It is found that the preferred orientations of ZnO films grown on GaAs substrates change with surface treatment condition of GaAS substrates. Moreover, optical qualities of the films depend on the growth temperature.
Section snippets
Experiment
ZnO thin films were grown on GaAs(0 0 1)substrates using MOCVD. Diethylzinc (DEZn) was used as the zinc precursor and high-purity oxygen gas (5 N) was used as the oxidizer. The reaction chamber and growth process have already been reported [13]. Ar was used as the carrier gas. N2 was used to prevent the source gases from upstreaming. In order to investigate effects of surface treatment of GaAS substrates on the growth of ZnO films, GaAs surfaces were etched in the mixture solution of a H2SO4:H2O2:H
Results and discussion
Fig. 1, Fig. 2 show XRD spectra of ZnO films grown at 630 °C on GaAs substrates etched under different conditions. As shown in Fig. 1, Fig. 2, only strong ZnO (0 0 2) diffraction peaks (34.45°) are observed when the etching times are 30 and 60 s, while more strong ZnO (1 0 0) diffraction peaks (31.7°) are observed when the etching times are 90 and 120 s.
ZnO (0 0 2), (1 1 0) and (1 0 0) planes have the low density of surface energy. The densities of the surface energy are (0 0 2), (1 1 0) and (1 0 0) in the low
Conclutions
ZnO films were grown by MOCVD on GaAs(0 0 1)substrates under different surface treatment conditions and at different growth temperatures. ZnO (0 0 2) films were grown on the GaAs substrate etching for less than 60 s, and ZnO (1 0 0) films were grown on the GaAs substrates etching for more than 90 s. It is found that the preferred orientation change of ZnO films occurs with the change of GaAs substrate treatment conditions. It is also found that the crystallinity of ZnO (1 0 0) film is better than ZnO (0 0
Acknowledgements
This work was supported by NSFC (No.60307002), 863 projects (No. 2003AA311080), Jilin University Young Teacher Foundation and Jilin University Innovation Foundation.
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