2016年7月27日星期三

Native oxides formation and surface wettability of epitaxial III–V materials: The case of InP and GaAs

Highlights

Wettability of binary, MOVPE grown, III–V materials (GaAs, InP, InAs) was investigated as a function of age and surface treatment.
XPS study was performed, to reveal the surface native oxides composition.
No trivial correlation between the oxide thickness/type and water drop contact angle was observed.

Abstract

The time dependent transition from hydrophobic to hydrophilic states of the metalorganic vapour phase epitaxy (MOVPE) grown InP, GaAs and InAs is systematically documented by contact angle measurements. Natural oxides forming on the surfaces of air-exposed materials, as well as the results of some typical wet chemical process to remove those oxides, were studied by X-ray photoemission spectroscopy (XPS), revealing, surprisingly, a fundamental lack of strong correlations between the surface oxide composition and the reported systematic changes in hydrophobicity.

Keywords

  • Hydrophobic surface
  • InP
  • GaAs
  • XPS
  • MOVPE
        • Source:Sciencedirect
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2016年7月26日星期二

Modification of electrical properties of Au/n-type InP Schottky diode with a high-k Ba0.6Sr0.4TiO3 interlayer

Highlights

Electrical properties of Au/Ba0.6Sr0.4TiO3/n-InP MIS diode have been analyzed.
Higher barrier height is obtained for the MIS diode compared to the MS diode.
Interface state density of MIS diode is lower than that of MS diode.
Poole-Frenkel mechanism is found dominating in both MS and MIS diodes.

Abstract

Au/Ba0.6Sr0.4TiO3 (BST)/n-InP metal/insulator/semiconductor (MIS) Schottky diodes have been analyzed by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The surface morphology of the BST films on InP is fairly smooth. The Au/BST/n-InP MIS Schottky diode shows better rectification ratio and low leakage current compared to the conventional Au/n-InP metal-semiconductor (MS) Schottky diode. Higher barrier height is achieved for the MIS Schottky diode compared to the MS Schottky diode. The Norde and Cheung's methods are employed to determine the barrier height, ideality factor and series resistance. The interface state density (NSS) is determined from the forward bias I-V data for both the MS and MIS Schottky diodes. Results reveal that the NSS of the MIS Schottky diode is lower than that of the MS Schottky diode. The Poole-Frenkel emission is found dominating the reverse current in both Au/n-InP MS and Au/BST/n-InP MIS Schottky diodes, indicating the presence of structural defects and trap levels in the dielectric film.

Keywords

  • High-k Ba0.6Sr0.4TiO3 insulating layer
  • n-type InP
  • MIS diode
  • Electrical properties;
  • Interface state density
  • Carrier transport mechanisms
        • Source:Sciencedirect
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2016年7月19日星期二

Easy adjustment structure and method for realizing InP based polarization beam splitter via Pockels effect dependence on crystal orientation

Abstract

We propose a novel adjustment structure and method for an InP-based polarization beam splitter/combiner by using the characteristic whereby the sign at the front of this term changes depending on the light propagation direction. To confirm the proposed principle of adjustment for our InP-based Mach–Zehnder interferometer polarization beam splitter/combiner, we fabricated a test sample that had an npin high-mesa waveguide structure with InGaAlAs/InAlAs multiple quantum wells. By using the test sample, we demonstrated the easy adjustment of an InP-based polarization beam splitter/combiner with the individual modulation of the TE and TM modes and showed that we can output TE/TM polarization at any port as desired.

Introduction

InP-based modulators/demodulators have become very attractive recently because of their small chip size, low driving voltage, and potential for monolithic integration with semiconductor active devices, such as laser/photo-diodes.110) And polarization-division multiplexing (PDM) is mainly used as a method for doubling the transmission capacity of digital coherent technology.110) Although several types of InP-based PDM components including a polarization beam splitter/combiner (PBS/PBC) have been reported,1122) there have been few reports regarding the monolithic integration of PBS/PBCs on InP-based modulators/demodulators.9,10)This is because the integration of InP-based PBS/PBCs is hindered by their tight fabrication tolerances caused by their higher refractive index. To overcome this, a promising way to realize monolithic integration is to activate phase shifters placed on the InP-based PBS/PBC. However, even this approach presents a difficulty and the adjustment takes a long time. Therefore, there is a real need for an easy adjustment method.
In this paper, we propose a novel structure for an InP-based PBS/PBC using a Mach–Zehnder interferometer (MZI) that allows the easy individual adjustment of the TE mode properties of the PBS/PBC. Our proposed structure and adjustment method provides a high yield PBS for monolithic integration. In Sect. 2, we point out the difficulty of fabricating a PBS/PBC on an InP waveguide. After an explanation of the refractive index changes in an InP waveguide when an electric field is applied, we propose a novel structure and principle for an easily adjustable InP-based PBS/PBC. In Sect. 3, we describe a test sample fabricated to verify our concept. We then confirm that the sign in front of the Pockels effect terms for the refractive index change depends on the light propagation direction by comparing the experimental and fitted data with an estimation of the linear and the quadratic electro-optic coefficients of the waveguides that we used in the test sample. In Sect. 4, we demonstrate the easy adjustment of the PBS/PBC properties by using the proposed structure and method23) and show that we can output TE/TM polarization at any desired port.

Keywords

  • InP; PDM
        • Source:iopscience
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