Zhu Shunming

High-quality ZnO growth, doping, and polarization effect

The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding (1) the development of high-quality epitaxy techniques, (2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and (3) the design, realization, and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an iso-valent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO. Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk.

Simulation and Suppression of the Gas Phase Pre-reaction in Metal-Organic Chemical Vapor Deposition of ZnO

The reaction mechanism and simulations of the metal-organic chemical vapor deposition reactor for ZnO film growth are presented, indicating the temperature of the reaction species. The gas phase pre-reaction can be modulated by several factors or conditions. Simulations verify the relationships between temperature and pyrolysis of precursors, and further reveal that the substrate temperature and flow rate of cooling water have great impacts on the temperature distribution. The experimental results agree with the simulations.

Photoelectric Properties of Si-Si1-xGex-Ge Heterostructures for Infrared Detector

Si-Si1-xGex-Ge heterostructures with Ge fraction graded linearly from 1 to 0 have been epitaxially grown on Ge substrates by rapid thermal process/very low pressure-chemical vapor deposition. The peak value of the spectrum response for these structures ranges from 1.3 to 1.55 ?m, which is just in accordance with the optical fiber communication window, and considered to be the superposition of the response in Si1-xGex absorption region and the Ge absorption region. High detecting sensitivity, and low dark current have been achieved from the prototype SiGe p-type intrinsic n-type photodetectors made of these structures.

First-Principles GGA+U Study of Intermediate-Band Characters from Zn1−xMxO (M = 3d Transition-Metal) Alloys Suitable for High Efficiency Solar Cell*

The electronic structure characters are calculated for the Zn1−xMxO alloys with some Zn atoms in ZnO substituted by 3d transition-metal atoms (M), in order to find out which of these alloys could provide an intermediate band material used for fabricating high efficiency solar cell. Especially, among of these alloys, the electronic structure character and optical performance of Zn1−xCrxO alloys clearly show an intermediate band filled partially and isolated from the VB and the CB in energy band structure of ZnO host, and the intermediate band characters can be preserved with increasing Cr concentrations no more than 8.33% in Zn1−xCrxO alloys, at the same time, the ratio 0.52 of EgFC to EgVF in Zn1−xCrxO, (x = 4.16%) alloy is closest to the optimal ratio of 0.57. Besides, compared to the ZnO, the optical absorption does indicate a great improved absorption below the calculated band gap of the ZnO and an enhancement of the optical absorption in the whole solar spectral energy range.

Study of influence of the vacuum annealing on physical properties of ZnMnO:N

Mn-N co-doped ZnO film on sapphire substrate was fabricated by metal-organic chemical vapor deposition (MOCVD) method, and the sample was annealed in vacuum under temperature 700℃, 900℃ and 1100℃, respectively. X-ray diffraction (XRD) displayed the vacuum annealing make the sample deteriorated, but showed the strong c-axis orientation. Raman and PL have been employed to analyze crystal qualities show the vacuum annealing makes oxygen vacancies ( V 0 ) increased. The first principle of simulation calculation for Mn and N codoped ZnO crystals have achieved, and the total density of states reveals the strong p-d interaction and existing magnetic moment in the Mn and N codoped ZnO. Once the introduction of oxygen vacancies ( V 0 ), the Fermi energy would be moved up, which resulted in p-d interaction disappear and magnetic moment reduced even disappeared. Therefore, the formation of magnetic bound polaron (BMP) of Mn 3d electronics and N 2p local bound electronic determines the magnetic interaction effects, which can be explained from the theoretical predication on the Mn 3d and N 2p ferromagnetic (hole) coupling on the ferromagnetism.

Sil−xGex/Si Multiple Quantum Well Wires Fabricated Using Selective Etching

Using lithography, and selective etching the Si 1-x Ge x /Si multiple quantum well wires are fabricated. The characteristics of the selective chemical etching of Si 1-x Ge x and Si are investigated, and high-performance etchants are developed. The etchant composed of HF:NH 4 F:H 2 0 2 :NH 4 OH is used for the etching of the epitaxial Si 1-x Ge x films, the selectivity is better than 250 for Si 0.76 Ge 0.24 , and increases with the increase of the mole fraction x of Ge. Another etchant composed of NH 4 NO 3 :NH 4 OH is used for the etching of Si, the selectivity is higher than 1000 ( x ≥ 0.1 ). A preliminary photoluminescence (PL) result obtained from the Si 0.76 Ge 0.24 multiple quantum well wires is presented. As the linewidth of the wires is reduced down to 50 nm, an intense complicated PL spectrum in the wavelength range of 500∼800 nm is observed at liquid nitrogen temperature. The origin of such spectrum is unclear.