Cui Deliang

Electrical properties and Raman spectra of undoped and Al-doped ZnO thin films by metalorganic vapor phase epitaxy

Abstract Undoped and Al-doped ZnO thin films have been deposited on Si substrates using metalorganic vapor phase epitaxy at atmospheric pressure. The as-deposited ZnO films showed good crystalline character and exhibited (002) orientation with the c axis perpendicular to the substrate surface. The carrier concentration of ZnO films was found to be dependent upon the doping of Al, and varied in the range from 10 19 to 10 20 cm −3 . The resistivity of ZnO films was in the order of magnitude of 10 −3 Ωcm. The Hall mobility decreased with the doping of Al and was in the range 5–53 cm 2 (V·s) −1 . Raman spectra indicated the observed A 1 (LO) and E 2 (high) bands shifted towards the low-frequency side.

Investigation on the key factors in the hydrothermal synthesis of BN: The way of introducing sodium azide

The way of introducing sodium azide (NaN3) into the reaction solution played an important role in the preparation of cBN by hydrothermal synthesis method. The results showed that both cBN content and crystalline perfection of the samples improved with increasing RN value, and pure cBN could be obtained at 300°C and 10 MPa when RN increased to 3:1. Here RN is defined as RN = NaN3(I)/NaN3(II), where NaN3(I) denotes the amount of NaN3 (in molar) that is added into the autoclave at the beginning of the reaction process, and NaN3(II) is the amount of NaN3 (also in molar) introduced into the autoclave at high temperature and high pressure (i.e. 300°C and 10 MPa). In order to explain the experimental results, a preliminary model was proposed in this paper.

A novel route to synthesize diphenylene by the catalytic effect of GaP nanocrystals

Diphenylene was synthesized directly from benzene under the catalytic effect of GaP nanocrystals, and the effect of GaP nanocrystals content was studied. The experimental results showed that no reactions took place without GaP nanocrystals. The more the GaP nanocrystals added, the more the reaction complete. Furthermore, at high temperatures (450–480°C), when the content of GaP nanocrystals was high enough, almost all benzene polymerized and the yield of diphenylene was rather high. On the contrast, even if there are enough GaP nanocrystals in the reaction mixture, almost no polymerization reaction took place at low temperature (for example, 250–300°C), and the yield of diphenylene was very poor. The analytical results of XRD, IR, elemental analysis and NMR proved that the sample was truly diphenylene.

Growth of AlxGa1−xP on GaAs substrate by metalorganic vapor phase epitaxy

The crystalline perfection of the AlxGa1−xP film grown on GaAs substrate by atmospheric pressure metalorganic vapor phase epitaxy has been studied using double-crystal X-ray diffraction and back-scattering spectrometry, and the behavior for the optical phonons of the AlxGa1−xP epilayer investigated by the Raman scattering technique. In addition, the reflection spectra in the visible-light spectra region from multilayer structures constructed by AlxGa1−xP/GaP pairs have been measured. The measurement of the full-width at half-maximum of the X-ray diffraction peak of the AlxGa1−xP epilayer showed that the crystalline perfection of the AlxGa1−xP film was improved by growing a GaP buffer layer and using a misoriented GaAs substrate. Corresponding to the temperature range 750–820°C, the higher crystalline perfection was obtained at the lower growth temperature. The value of the minimum yield of back-scattering spectrometry of Al0.24Ga0.76P/GaAs (3.4×10−2) revealed that the epilayer was not perfect and contained both elastic strain and misfit dislocations. A two-mode Raman characteristic of Al0.21Ga0.79P/GaAs was clearly seen with two LO modes, AlP-like LO and GaP-like LO located at 460 and 392 cm−1, respectively. For the (Al0.21Ga0.79P)10/(GaP)10 structure, a reflectivity above 60% was realized.

Effect of Pressure on Thermal Stability and Decomposition of KDP Crystal

Effect of pressure on thermal behavior of KDP crystals is investigated by using the in-situ infrared reflective spectra. Compared with that under normal atmosphere, the onset temperature of decomposition under pressure of 1 MPa is improved to from 210°C to 213°C, suggesting that the thermal stability of KDP is enhanced. Under pressure of 2 MPa, the thermal stability is deteriorated and KDP begins to decompose at 183°C. Under normal atmosphere KDP decomposes in route of translating to K4P2O7 firstly, and then to KPO3. Under pressures of 1 MPa and 2MPa, KDP translates to KPO3 directly without any other polymeric intermediates.

Crystal characterization of GaP epilayer grown on GaAs by atmospheric pressure metalorganic vapor phase epitaxy

The crystal perfection in GaP film grown on GaAs by atmospheric pressure metalorganic vapor phase epitaxy has been studied by the use of double crystal X-ray diffraction, backscattering spectrometry and Raman scattering techniques. By means of the morphology and full-width at half maximum of X-ray diffraction peak for the GaP epilayers, the growth temperature and V/III ratio were optimized. In the temperature range from 720 to 800°C and with the V/III ratio range from 10 to 80, it was concluded that the optimum growth temperature was 800°C with a V/III ratio of approximately 15. The result of backscattering spectrometry revealed that the minimum yield for the GaP epilayer grown under nearly optimized growth conditions exceeded that for a perfect crystal. In addition, the residual strain of GaP epilayer was calculated by using a biaxial stress model and Raman scattering measurement.