Study on the Effect of Oxygen Defects on the Electrical and Optical Properties of Thin Films

SnO2 thin films grown directly on the Si substrate had larger average grain sizes as the power intensity increased, but the average grain size of the SnO2 thin films grown in oxygen atmosphere decreased as the power intensity increased. Hall measurement of pure SnO2 thin films showed that the carrier density increased with increasing power. However, upon annealing the SnO2 thin films, the carrier density decreased with increasing power owing to the formation of oxygen vacancies and the SiO2 layer between the Si substrate and SnO2 thin films. The photoluminescence (PL) of the SnO2 thin film grown in the oxygen atmosphere changed, and it was affected by the oxygen defects at the surface and interfaces of the thin film.

Photoluminescence in Analysis of Surface and Interfaces of Semiconductor Nanostructures

The intensity and excitation energy is chosen for different materials to probe different regions and excitations concentrations in the sample. The intensity of the PL signal provides information on the quality of surfaces and interfaces. Also, information on the electronic bands structure and the SC Energy gap can be obtained, as well as thermodynamics quantities such as temperature. For this experiment we just compared the photoluminescence (PL) spectra of AlGaAs/GaAs quantum wells (QWs) with different well widths (100 Å and 85 Å) and InAs/GaAs quantum dots (QD) structures as well as the theoretical aspects were covered. The sample are held in a cryostat and excited by a Helium-Neon laser. The emitted light is then captured by an optical fiber plugged to a spectrometer The optical fibre is plugged to a spectrometer equipped with a CCD detector, driven by a computer allowing us to acquire data. And this was used to avoid interaction between charge carriers and thermally excited phonons, it was used cryogenic temperature around 2k to cool the sample. simply with the theoretical models this experiement allows to collect numerous information about the lowest band to band transition in semiconductor materials.and for quantum dots which was the last sample in this study couldn’t be resolved individually.

Realtime X-ray reflectometry to see changes at buried interfaces

X-ray reflectometry is powerful in determining internal structure of multilayered thin films, such as thickness and density of each layer, as well as the roughness of surface and interfaces [1]. The measurement requires some precise angular scans near the critical angle with monochromatic parallel X-rays, and therefore it has not been thought that the technique is basically suitable to see changes. However, even without any angular scans, it is possible to obtain essentially the same data by using wide angular dispersion of the incident X-ray beam. The principle is basically known as Naudon's pioneering concept [2]. The system has been improved further by employing a monochroator, which was not used by Naudon's work. A multilayer monochromator was placed at very narrow limited space between a rotating anode X-ray source and the sample stage [3]. Use of a fast Si strip detector also contributed to improve the time-resolution. One can obtain an X-ray reflectivity curve with 4.5 decades even in 1 sec. It is possible to measure the curve down to 10-6, if 20 sec accumulation is allowed. Another advantage of the present instrument is fairly wide angular divergence, which ensures simultaneous data collection for 2 deg range. One of our recent successful applications of this method is the measurement of thermal expansion factor of the polymer thin film. It was also possible to see melting and freezing surfaces. In the presentation, such practical application will be demonstrated, in addition to the detailed description of our instruments.