Preparation Of ZnMgO Alloy Films, Li-N Co-doped P-type ZnO Thin Flims By Pulsed Laser Deposition And Fabrication Of ZnO UV Detector

ZnO is a â…¡-â…¥ compound semiconductor with a direct wide band gap of 3.3 eV. Its crystal structure, lattice parameter and band gap are quite close to those of GaN. The most significant advantage of ZnO lies in its extremely large exciton binding energy, about 60 meV, over double than that of GaN, which allows stimulated excitonic emission at room temperature or even higher temperature. Therefore, ZnO is a potential candidate for applications in short-wave optoelectronic devices, such as bule/violet light emitting diodes and laser diodes.Zn_1-xMg_xO alloy thin films and ZnO/Zn_1-xMg_xO heterostructures on silicon, as well as p-type Zn_1-xMg_xO and ZnO thin films, were prepared by home-made pulsed laser deposition (PLD). In addition, a photoconductive ultraviolet detector based on ZnO films grown by PLD was fabricated on silicon. The crystalline quality and photoluminescent properties of the ZnO/Zn_1-xMg_xO heterostructures on silicon were investigated for exploiting ZnO-based optoelectronic devices. In this work, low resistivity p-type ZnO thin films were realized via a new kind of co-doping method, Li-N co-doping. 1. Zn_1-xMg_xO alloy thin films and ZnO/Zn_1-xMg_xO heterostructures on siliconHigh-quality Zn_1-xMg_xO alloy thin films with c-axis preferred orientation were grown on p-Si(100) by PLD. The alloy thin films had the same crystal structure with ZnO. The film prepared under optimized condition was highly crystalline, with a surface roughness of ¹ run and a small lattice mismatch with ZnO of -0.35%.ZnO/Zn_1-xMg_xO double heterostructures (DHs) were firstly fabricated on Si(lOO) and ZnO/Si(100) by PLD, respectively. The near band emission (-3.29 eV) from the ZnO layer in DHs was observed in the room-temperature photoluminescence sprectum. The deep level emission was quite weak, indicating high crystalline quality of the DHs. ZnO/Zn_1-xMg_xO multi-quantum wells (MQWs) with ten period were also firstly attempted to grow on ZnO/Si(100).p-type Zn_1-xMg_xO thin films were firstly realized by PLD via Li mono-doping.The lowest resistivity was 10.1 Qcm, with a high hole concentration of 2.45xl018cm"3, and a Hall mobility of 0.251 cm2/Vs.2. Li* N double-acceptor codoping p-type ZnO thin filmsLow-resistivity p-type ZnO thin films were successfully fabricated by Li-N dual-acceptor doping method employing PLD. ZnO:Li ceramics with different Li content were used as Li agent and high-voltage ionized N2O was used as N source.Process parameters were optimized for Li-N codoping p-type ZnO thin films. The lowest resistivity of p-ZnO:(Li,N) thin films was 3.99 Qcm, with a high hole concentration of 9.12xl018cm3, and a Hall mobility of 0.172 cm2/Vs. The film was prepared at 450 °C with a pulsed laser fluence of 300 mJ, and a N2O pressure of 15 Pa with an ionizing power of 3.5 W. Li content in the target was 0.1 at%.There were four emission bands in 10 K PL spectrum of p-ZnO:(Li,N) thin film. The bands located at 3.374 eV, 3.318 eV, 3.215 eV and 3.154 eV, respectively, which were probably due to neutral acceptor bound exciton (A°X) and three donor-acceptor (DAP) transitions. The corresponding related acceptor levels of the three (DAP) transition were calculated to be -120 meV, -222 meV, and -283 meV, respectively. The levels located at -120 meV and -222 meV were assigned to Li acceptor and N acceptor respectively.Furthermore, physical mechanism of Li-N dual-acceptor doping was discussed and a co-doping model was proposed.3. ZnO photoconductive UV detector on siliconHigh-resistivity ZnO thin film with completely c-axis orientation was grown on Si(lll) by PLD. A photoconductive ultraviolet detector was fabricated based on this ZnO film with an M-S-M structure. Al was used as planar interdigital metal electrodes. The cutoff wavelength of Al-ZnO-Al ultraviolet detector was 370 nm, and its photoresponsivity was 0.5 A/W at 5 V bias.