Sang-heon Lee

Effects of in doping on structural and optical properties of ZnO nanorods grown by hydrothermal method

ZnO seed layers were deposited on a quartz substrate using the sol-gel method, and In-doped ZnO (IZO) nanorods with different In concentrations ranging from 0 to 2.0 at. % were grown on the ZnO seed layers by the hydrothermal method. The structural and optical properties of the ZnO and IZO nanorods were investigated using field-emission scanning electron microscopy, x-ray diffraction (XRD), and photoluminescence (PL). The ZnO and IZO nanorods grew well aligned on the surface of the quartz substrates. From the XRD data, it can be seen that the In doping is responsible for the distortion of the ZnO lattice. The PL spectra show near-band-edge emission and deep-level emission, and they also show that In doping significantly affects the PL properties of ZnO nanorods.

Optical Properties of ZnO Soccer-Ball Structures Grown by Vapor Phase Transport

ZnO soccer balls were grown on an Au-catalyzed Si(100) substrate by vapor phase transport (VPT) with a mixture of zinc oxide and graphite powders. Temperature-dependent PL was carried out to investigate the mechanism governing the quenching behavior of the PL spectra. From the PL spectra of the ZnO soccer balls at 10 K, several PL peaks were observed at 3.365, 3.318, 3.249, and 3.183 eV corresponding to excitons bound to neutral donors (DoX), a donor–acceptor pair (DAP), first-order longitudinal optical phonon replica of donor–acceptor pair (DAP-1LO), and DAP-2LO, respectively. The mixed system composed of the free exciton (FX) and DoX and the DAP radiative lifetimes were estimated with a theoretical relation between the lifetime and the spectral width. The exciton radiative lifetimes were observed to increase linearly with temperature.

Optical and structural prorerties of InAs epilayer on graded InGaAs

We have studied infrared photoluminescence (PL) and x-ray diffraction (XRD) of 400 nm and 1500 nm thick InAs epilayers on GaAs, and 4 nm thick InAs on graded InGaAs layer with total thickness of 300 nm grown by molecular beam epitaxy. The PL peak positions of 400 nm, 1500 nm and 4 nm InAs epilayer measured at 10 K are blue-shifted from that of InAs bulk by 6.5, 4.5, and 6 meV, respectively, which can be largely explained by the residual strain in the epilayer. The residual strain caused by the lattice mismatch between InAs and GaAs or graded InGaAs/GaAs was observed from XRD measurements. While the PL peak position of 400 nm thick InAs layer is linearly shifted toward higher energy with increase in excitation intensity ranging from 10 to 140 mW, those of 4 nm InAs epilayer on InGaAs and 1500 nm InAs layer on GaAs is gradually blue-shifted and then, saturated above a power of 75 mW. These results suggest that adopting a graded InGaAs layer between InAs and GaAs can efficiently reduce the strain due to lattice mismatch in the structure of InAs/GaAs.