Browsing by Author "Wan, Lingyu"

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Evolution of the local structure and crystal phase for thin ZnGaO films grown by metal organic chemical vapor deposition
(2019-08-15)
Lin, Xiwen
;
Chen, Daihua
;
Niu, Wenlong
;
Huang, Chiung-Yi
;
Horng, Ray Hua
A systematic investigation is reported to comprehend the atomic and crystal structure of several thin ZnGaO films grown by metal organic chemical vapor deposition method using different flow rates of diethylzinc (DEZn) while keeping triethylgallium and oxygen flow rates constant. The x-ray absorption fine structure analysis has indicated that the local structure of Ga absorbing atom is close to that of beta-Ga2O3 at a lower DEZn flow rate of 30 sccm and transforming to ZnGa2O4 structure at higher 60 sccm. There is a certain proportion of Ga ions that occupies the tetrahedral sites. The ratios of tetrahedral and octahedral Ga species (Ga(t)/Ga(o)) are found to be within 5.5-8.8%. The x-ray diffraction patterns showed the crystal structure of ZnGaO films gradually evolving from monoclinic to cubic phase with an increase of DEZn flow rates from 30 sccm to 60 sccm. One film prepared at 40 sccm displays the best crystalline quality and the other grown at 50 sccm exhibits excellent smooth surface having the lowest root mean square value with a roughness of 0.42 nm. The correlation between atomic and crystal structure and the growth is helpful to understand the formation of single-crystalline ZnGa2O4 and its physical mechanism.
Green Light-emitting Diodes with InGaN/GaN Multiple Quantum Well Structures: Time-resolved Photoluminescence, Emission Dynamics and Related Studies
(2016)
Feng, Zhe Chuan
;
Jiang, Xiaodong
;
Lee, Yueh-Chien
;
Kuo, Hao-Chung
;
Wan, Lingyu
To explore the mechanism, breakthrough the current bottleneck and overcome the efficiency droop from green InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs). The photoluminescence properties and carrier dynamics of green InGaN/GaN MQW LEDs are investigated by temperature-dependent photoluminescence (PL) from 10 K to 300 K and time-resolved PL (TRPL) measurements at 10 K in our new-built lab. With increasing temperature, a blue shift of PL behavior is attributed to band-tail states formed in local potential minima resembling In-rich clusters. The energy-dependent TRPL experiments are measured at 10 K to study the carrier dynamics in the MQWs. The results show that the PL slow decays for the low-energy side are much slower than the high-energy side. The depth of carrier localization is obtained by fitting the reduced slow decay time with the emission energy increasing. All the results indicate that the PL peak is related to localized radiative recombination.
Modelling of microcavity effect in InGaN/GaN heterostructures for interfacial study
(2018-08-01)
Liu, Honghui
;
Lin, Tao
;
Wan, Lingyu
;
Xu, Gu
;
Kuo, Hao-Chung
Photoluminescence (PL) spectrum provides the most conventional measurement for emission properties of GaN-based light-emitting diodes (LEDs), in which Fabry-Perot oscillations are often observed modulating the emission peaks. A fitting model for PL intensity accounting the microcavity between air/GaN and GaN/sapphire heterostructure was proposed to treat the PL spectra of different GaN-based LEDs, extracting key factors that implied the interfacial optical properties. This approach was successfully verified by measurements of spectroscopic ellipsometry, then was applied to quantitatively analyse the interfacial-defect-related distortion of dielectric properties. The extracted oscillation coefficient is sensitive to the change of interface qualities and reveals the optical properties of internal interfaces. The new method may also be applied to the other heterojunction LEDs.