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Pressure effect on impurity local vibrational mode and phase transitions in n-type iron-doped indium phosphide.

ABSTRACT: The evolution of iron local vibrational mode (Fe LVM) and phase transitions in n-type iron-doped indium phosphide (InP:Fe) were investigated at ambient temperature. In-situ angle-dispersive X-ray diffraction measurements revealed that InP:Fe starts to transform from zinc-blende (ZB) to rock-salt (RS) structure around 8.2(2) GPa and completes around 16.0(2) GPa. The Raman shift of both transverse and longitudinal optical modes increases monotonically with increasing pressure, while their intensities become indiscernible at 11.6(2) GPa, suggesting that the pressure-induced phase transition is accompanied by significant metallization. In contrast, originally absent at ambient pressure, the Raman shift of Fe LVM appears at ?420?cm-1 near 1.2?GPa and exhibits a dome shape behavior with increasing pressure, reaching a maximum value of ?440?cm-1 around 5?GPa, with an apparent kink occurring around the ZB-RS transition pressure of ?8.5(2) GPa. The Fe K-edge X-ray absorption near edge structure (XANES) confirmed the tetrahedral site occupation of Fe3+ with a crystal field splitting parameter ? t ?=?38?kJ·mole-1. Our calculations indicate that the energy parameters governing the phase transition are ?t?=?0.49 and ? o ?=?1.10?kJ·mole-1, respectively, both are much smaller than ? t ?=?38?kJ·mole-1 at ambient.

SUBMITTER: Lin CM

PROVIDER: S-EPMC5775340 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Pressure effect on impurity local vibrational mode and phase transitions in n-type iron-doped indium phosphide.

Lin Chih-Ming CM Hsu I-Jui IJ Lin Sin-Cheng SC Chuang Yu-Chun YC Chen Wei-Ting WT Liao Yen-Fa YF Juang Jenh-Yih JY

Scientific reports 20180119 1

The evolution of iron local vibrational mode (Fe LVM) and phase transitions in n-type iron-doped indium phosphide (InP:Fe) were investigated at ambient temperature. In-situ angle-dispersive X-ray diffraction measurements revealed that InP:Fe starts to transform from zinc-blende (ZB) to rock-salt (RS) structure around 8.2(2) GPa and completes around 16.0(2) GPa. The Raman shift of both transverse and longitudinal optical modes increases monotonically with increasing pressure, while their intensit ...[more]

PMID: 29352141

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Project description:The large bulk bandgap (1.35 eV) and Bohr radius (~10 nm) of InP semiconductor nanocrystals provides bandgap tunability over a wide spectral range, providing superior color tuning compared to that of CdSe quantum dots. In this paper, the dependence of the bandgap, photoluminescence emission, and exciton radiative lifetime of core/shell quantum dot heterostructures has been investigated using colloidal InP core nanocrystals with multiple diameters (1.5, 2.5, and 3.7 nm). The shell thickness and composition dependence of the bandgap for type-I and type-II heterostructures was observed by coating the InP core with ZnS, ZnSe, CdS, or CdSe through one to ten iterations of a successive ion layer adsorption and reaction (SILAR)-based shell deposition. The empirical results are compared to bandgap energy predictions made with effective mass modeling. Photoluminescence emission colors have been successfully tuned throughout the visible and into the near infrared (NIR) wavelength ranges for type-I and type-II heterostructures, respectively. Based on sizing data from transmission electron microscopy (TEM), it is observed that at the same particle diameter, average radiative lifetimes can differ as much as 20-fold across different shell compositions due to the relative positions of valence and conduction bands. In this direct comparison of InP/ZnS, InP/ZnSe, InP/CdS, and InP/CdSe core/shell heterostructures, we clearly delineate the impact of core size, shell composition, and shell thickness on the resulting optical properties. Specifically, Zn-based shells yield type-I structures that are color tuned through core size, while the Cd-based shells yield type-II particles that emit in the NIR regardless of the starting core size if several layers of CdS(e) have been successfully deposited. Particles with thicker CdS(e) shells exhibit longer photoluminescence lifetimes, while little shell-thickness dependence is observed for the Zn-based shells. Taken together, these InP-based heterostructures demonstrate the extent to which we are able to precisely tailor the material properties of core/shell particles using core/shell dimensions and composition as variables.

Dataset Information

Pressure effect on impurity local vibrational mode and phase transitions in n-type iron-doped indium phosphide.

Publications

Pressure effect on impurity local vibrational mode and phase transitions in n-type iron-doped indium phosphide.

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