The Preparation Of Ge Quantum Dots Detecting Material By Using Ion Beam Sputtering And The Preliminary Investigation On The Device

Recently, the fabrication and property characterization of Ge quantum dots (QDs) become one of the focus topics in research field due to its novel quantum confinement effect and excellent optoelectronic properties. The growth morphology and optoelectronic properties of Ge quantum dots (QDs) photodetectors based on SiO2/Si substrate have been studied in this paper. The Ge QDs morphology and crystallinity were investigated by using atomic force microscope (AFM), Raman spectrum and FTIR. The effect of sputtering growth parameters and surface morphology of Ge QDs on optoelectronic properties were discussed. The preparation of detector electrode and the electrical properties of the detector were also investigated by scanning electron microscope (SEM) and I-V test, respectively. The main contents are as following:(1) Based on the growth parameters of Ge QDs which are explored in the early stage of laboratory, we compared the difference of Ge/Si layer on the SiO2/Si substrate and on the SOI (Silicon-On-Insulator) substrate by using ion beam sputtering deposition (IBSD). The AFM results show that the SiO2/Si substrate is more suitable for the growth of Ge QDs when the Si channel layer is thin, the fabricated Ge QDs can be used as fundamental structures as the subsequent device preparation. The QDs grown at 700℃ show a good uniformity of sizes and morphology. The density of ordered Ge QDs deposited at 700℃ on the SiO2/Si substrate can reach 1010/cm2. On the other hand, the density of QDs can be changed with the thickness of Si layer. When the thickness reach to 20nm, the density of Ge QDs is the highest, however, with increasing Si layer thickness, the dots density decreases again.(2) The electrodes of detectors were prepared by using magnetron sputtering technology. The effects of different annealing methods on the surface morphology, surface roughness and electrical properties of the electrodes have been analyzed, respectively. Compared with other annealing methods, the in-situ annealing can make electrodes dense and smooth. Meanwhile, the I-V curve results obtained is more practical.That is to say, the electrodes prepared by in-situ annealing are more suitable for the fabrication of the optoelectronic detectors.(3) The electrical and optical properties of Ge quantum dot photodetectors were also studied. According to the test of I-V performance, it is found that the Ge QDs photodetector is more sensitive to near-infrared light than to visible light. Meanwhile, under the same wavelength of light irradiation, the more the power of incident light, the more the photocurrent measurement. By tuning the gate voltage, the performance of device can be modulated effectively. The results show that with increasing the gate voltage in positive range, the photocurrent of device decreases; instead, with the increase of negative gate voltage, the photocurrent is enhanced. The optical properties of device were characterized by FTIR spectra. It indicates that the structure fabricated by us shows two obvious absorption peaks at 5.8um and 3.4um, respectively. The typical peak at 5.8um is assigned to the transition between two heavy holes energy levels in Ge QDs. The other peak at 3.4um is assigned to the holes transition from the ground state level of Ge QDs to the valance band edge of Si. The absorption for infrared light of the device demonstrates its possibility of being the infrared detector in the future.