Near-resonant high order nonlinear absorption of ZnO thin films

Yun-Pei Chan,Chih-Chang Hsu,Wen-Feng Hsieh,Ja-Hon Lin

doi:10.1364/oe.16.019900

Abstract

Nonlinear optical absorption of ZnO thin film grown by the laser molecular beam epitaxy was investigated by the Z-scan method using a frequency-doubled femtosecond Ti:sapphire laser. Due to near-exciton resonance, an enormous enhancement of two photon absorption (TPA) is about 3000 cm/GW at 390 nm which is about 6.5 times larger than the previously reported at two-photon exciton resonance in near-IR regime and 710 times larger than that of ZnO bulk measured at 532 nm. Besides, the free-carrier absorption resulting from linear absorption and TPA becomes essential when the excitation approaches the exciton resonance.

Highlights

ZnO, a kind of II-VI compound semiconductor, has been a potential candidate of ultraviolet (UV) photonic devices due to its wide bandgap of 3.37 eV and a relative large exciton binding energy (Eb) of about 60 meV at room temperature (RT), which is much higher than that of ZnSe (20 meV) and GaN (27 meV)
The high exciton binding energy permits excitonic recombination even at RT that can be a potential candidate for UV laser diode [1]
In this paper we focus on the optical nonlinear absorption of ZnO thin film near resonant to its band-gap by using the Z-scan method

Summary

Introduction

ZnO, a kind of II-VI compound semiconductor, has been a potential candidate of ultraviolet (UV) photonic devices due to its wide bandgap of 3.37 eV and a relative large exciton binding energy (Eb) of about 60 meV at room temperature (RT), which is much higher than that of ZnSe (20 meV) and GaN (27 meV). Research on the photoluminescence (PL) properties of ZnO nanostructures has shown that, under high excitation conditions, exciton-exciton scattering as well as the recombination of electron-hole plasma is the key process leading to stimulated emission and lasing [2]. These studies demonstrated the potential of using ZnO to fabricate RT UV laser [3]. A comprehensive review on the synthesis, mechanical, chemical, thermal and optical properties of ZnO may be found in Ref. [4]

Methods

Results

Conclusion