Enhanced Photodetection with Crystalline Si Nanoclusters

SiO_x nanodots were fabricated on a TiO₂ thin film using glancing angle deposition technique. The fabricated samples were annealed at 950 °C in open air configuration to obtain Si nanoclusters resulting from phase separation of SiO_x nanodots. Field Emission Gun Scanning electron microscopy and atomic force microscopy were used to examine the topography of the samples. The elemental composition of the samples was analyzed using energy dispersive X-ray mapping and their crystallinity was confirmed by analyzing the bandgap determined from the Tauc plots. The annealed samples show a broadband absorption which is about two folds in magnitude as compared to the as deposited (unannealed) samples. The photoluminescence spectra confirms the quantum confinement effect in the annealed samples. A photodetector was fabricated from an annealed sample by depositing gold contacts on top of it. This photodetector showed a two-fold increase in dark current and a 1.5-fold increase in light current compared to a photodetector made from the as-deposited SiO_x samples-which is due to the increased crystallinity in Si nanoclusters. Finally, the rise and fall times of the device were measured through a switching experiment.

Improved UV Photodetection by Indium Doped TiO₂ Thin Film Based Photodetector

Indium (In) was doped into TiO2 thin film (TF) using the electron beam evaporation technique followed by an annealing process. The high resolution X-ray diffraction (HRXRD) analysis revealed lower angle diffraction peak (2) shifting of Rutile (002) phases of TiO2 from 61.9 to 61.56 for an increased In doped samples. Calculated average grain size from FESEM (field emission scanning electron microscope) gradually decreased from 21.12 nm to 17.03 mm with an increase in In content ranging from 1.45~17.30 at%. HRXRD data revealed that crystallite sizes also reduced from 21.79 nm to 16.93 nm with an increased In doping concentration. Doping of In leads to the formation of inhomogeneous InxTiy O2 alloy that enhances the transition between 3.3-3.42 eV energy levels with variation in doping concentration. The photo-efficiencies for increased doping concentration of In with 3.47 at% and 17.30 at% were enhanced by 2.56 and 2.76 times, respectively, compared to the undoped TiO2 TF detector and both were larger than low doped In with 1.45 at% sample. The ratio of main band detection intensity to oxygen defect level was also increased from 0.22 to 2.22 with the gradual increase in In content.

Improved Photo-Detection Using Zigzag TiO2 Nanostructures as an Active Medium

Zigzag TiO2 nanostructures were fabricated using oblique angle deposition technique. The field emission gun-scanning electron microscope (FEG-SEM) image shows that the TiO2 zigzag nanostructures were ~500 nm in length. Averagely two times enhanced UV-Vis absorption was recorded for zigzag structure compared to perpendicular TiO2 nanowires. The main band transition was observed at ~3.4 eV. The zigzag TiO2 exhibited high turn on voltage (+11 V) than that of nanowire (+2 V) detector under dark which were reduced to +0.2 V and +1.0 V under white light illumination, respectively. A maximum ~6 fold photo-responsivity was observed for the zigzag TiO2 compared with nanowire device at + 1.0 V applied potential. The maximum photo-responsivity of 0.36 A/W at 370 nm was measured for the zigzag TiO2 detector. The TiO2 zigzag detector showed slow response with rise time of 10.2 s and fall time of 10.3 s respectively. The UV (370 nm) to visible (450 nm) wavelength rejection ratio of photo-responsivity was recorded ~4 times for the detector.