| First principle electroabsorption calculations based on WTK spectral density theorem and Dow and Redfield theory were performed and used as the basis of a model to fit experimental electroabsorption data. The calculation results were compared to absorption measurements taken from 4.5 K to 300 K on a c-plane ZnO thin film sample to obtain the temperature broadening linewidth. The extracted broadening parameters were then expressed with two material related coefficients: the exciton-acoustic-phonon interaction strength gammaph = 79.6 +/- 3 microeV/K and exciton-LO-phonon interaction strength Gamma LO G = 242 +/- 10 meV. This expression is independent of sample qualities, or is "generalized" to accommodate the exciton band edge. A concept called "effective microfield intensity" was introduced to represent the crystalline quality. The microfield intensities of two ZnO samples with rocking curve FWHMs ∼ 0.25° and ∼ 0.42° are ∼ 1.3x105 and ∼ 2.26x105 kV/cm respectively.; Buffer-assisted growth technique was applied to improve the quality of PLD grown ZnO on sapphire. ZnO thin films were deposited on ATO/ITO/glass substrate at 500 to 700 K, with higher temperature producing better films. XRD of these samples show highly c-oriented ZnO growth on the ATO substrate.; ZnO electroabsorption modulators were fabricated based on ZnO/ATO/ITO/glass structure. Two types of top electrodes, Ni semi-transparent electrode (TE) and conducting indium gallium zinc oxide (IGZO) were experimented with the IGZO-coated device reducing the insertion loss by ∼50%. The DC percentage modulation of these devices have two peaks, over 40% near ∼ 370 nm and around 20% near ∼ 385 nm at 140 V bias. AC testing confirms purely field modulation and shows no evident of frequency cut-off up to 100 kHz. A simple device model attributes the threshold voltage of ZnO electroabsorption modulators to the charge screening effects. Applied voltage was obtained both by converting the electric field based on device model and fitting the observed electroabsorption spectra with the first principle calculation and Gaussian broadening. The field strengths obtained from the two approaches is consistent. |
