Wurtzite InN nanodots on Si(100) by molecular beam epitaxy

Studies were carried on the growth behavior of InN nanodots by plasma assisted molecular beam epitaxy on bare Si(100) substrates and their structural, optical, electrical properties. The growth was carried out by two different methods such as, (i) mono-step growth process at a low temperature and a (ii) bi-step growth process with the combination of low and high temperatures for the formation of single crystalline nanodots with well defined crystallographic facets due to cluster migration. Low temperature photoluminescence shows a free excitonic (FE) luminescence at 0.80 eV. The Raman spectroscopy and X-ray diffraction studies reveal that the nanodots as well as the film were of wurtzite structure and strain free.

Determination of wurtzite InN/cubic In2O3 heterojunction band offset by x-ray photoelectron spectroscopy

In2O3 is a promising partner of InN to form InN/In2O3 heterosystems. The valence band offset (VBO) of wurtzite InN/cubic In2O3 heterojunction is determined by x-ray photoemission spectroscopy. The valence band of In2O3 is found to be 1.47 +/- 0.11 eV below that of InN, and a type-I heterojunction with a conduction band offset (CBO) of 0.49-0.99 eV is found. The accurate determination of the VBO and CBO is important for use of InN/In2O3 based electronic devices.

Determination of the valence band offset of wurtzite InN/ZnO heterojunction by x-ray photoelectron spectroscopy

The valence band offset (VBO) of the wurtzite InN/ZnO heterojunction is directly determined by x-ray photoelectron spectroscopy to be 0.82 +/- 0.23 eV. The conduction band offset is deduced from the known VBO value to be 1.85 -/+ 0.23 eV, which indicates a type-I band alignment for InN/ZnO heterojunction. (C) 2007 American Institute of Physics.

Study of band offsets in InN/Ge heterojunctions

InN layers were directly grown on Ge substrate by plasma-assisted molecular beam epitaxy (PAMBE). The valence band offset (VBO) of wurtzite InN/Ge heterojunction is determined by X-ray photoemission spectroscopy (XPS). The valence band of Ge is found to be 0.18 +/- 0.04 eV above that of InN and a type-II heterojunction with a conduction band offset (CBO) of similar to 0.16 eV is found. The accurate determination of the VBO and CBO is important for the design of InN/Ge based electronic devices. (C) 2011 Elsevier B.A. All rights reserved.

Indium flux, growth temperature and RF power induced effects in InN layers grown on GaN/Si substrate by plasma-assisted MBE

In the present work, we report the growth of wurtzite InN epilayers on GaN/Si (1 1 1) substrate by plasma-assisted molecular beam epitaxy (PAMBE). The growth parameters such as indium flux, substrate temperature and RF power affect the crystallographic and morphological properties of InN layers, which were evaluated using high resolution X-ray diffraction (HRXRD) analysis and atomic force microscopy (AFM). It is found that excess indium (In) concentrations and surface roughness were increased with increase in In flux and growth temperature. The intensity of HRXRD (0 0 0 2) peak, corresponding to c-axis orientation has been increased and full width at half maxima (FWHM) has decreased with increase in RF power. It was found that highly c-axis oriented InN epilayers can be grown at 450 degrees C growth temperature, 450 W RF power and 1.30 x 10(-7) mbar In beam equivalent pressure (BEP). The energy gap of InN layers grown by optimizing growth conditions was determined by photoluminescence and optical absorption measurement. (C) 2011 Elsevier B.V. All rights reserved.

Transport and infrared photoresponse properties of InN nanorods/Si heterojunction

The present work explores the electrical transport and infrared (IR) photoresponse properties of InN nanorods (NRs)/n-Si heterojunction grown by plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN NRs is verified by the X-ray diffraction and transmission electron microscopy. Raman measurements show that these wurtzite InN NRs have sharp peaks E(2)(high) at 490.2 cm(-1) and A(1)(LO) at 591 cm(-1). The current transport mechanism of the NRs is limited by three types of mechanisms depending on applied bias voltages. The electrical transport properties of the device were studied in the range of 80 to 450 K. The faster rise and decay time indicate that the InN NRs/n-Si heterojunction is highly sensitive to IR light.

Research on the band-gap of InN grown on siticon substrates

Photoluminescence (PL) and absorption experiments were carried out to examine the fundamental band-gap of InN films grown on silicon substrates. A strong PL peak at 0.78 eV was observed at room temperature, which is much lower than the commonly accepted value of 1.9 eV. The integrated PL intensity was found to depend linearly on the excitation laser intensity over a wide intensity range. These results strongly suggest that the observed PL is related to the emission of the fundamental inter-band transitions of InN rather than to deep defect or impurity levels. Due to the effect of band-filling with increasing free electron concentration, the absorption edge shifts to higher energy. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

InN layers grown by MOCVD on SrTiO3 substrates

Epitaxial wurtzite InN thin films have been grown by metal-organic chemical vapor deposition on (1 1 1) SrTiO3 (STO) substrates. Interestingly, twin domain epitaxy induced by the surface reconstruction of STO is observed with the in-plane orientation relationships of [(1) over bar 1 0 0]InN parallel to [<(1)over bar > 1 0]STO and [2 <(1 1)over bar > 0]InN parallel to[<(1)over bar > 1 0]STO, which is helpful to release the strain. The InN films on STO substrates exhibit a strong photoluminescence emission around 0.78 eV. Particularly, using STO substrates opens up a possibility to integrate InN with the functional oxides. (C) 2009 Elsevier B.V. All rights reserved

Structural, electronic, and optical properties of wurtzite and rocksalt InN under pressure

Structural stability, electronic, and optical properties of InN under high pressure are studied using the first-principles calculations. The lattice constants and electronic band structure are found consistent with the available experimental and theoretical values. The pressure of the wurtzite-to-rocksalt structural transition is 13.4 GPa, which is in an excellent agreement with the most recent experimental values. The optical characteristics reproduce the experimental data thus justifying the feasibility of our theoretical predictions of the optical properties of InN at high pressures.

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

InN Quantum Dot Based Infra-Red Photodetectors

Self-assembled InN quantum dots (QDs) were grown on Si(111) substrate using plasma assisted molecular beam epitaxy (PA-MBE). Single-crystalline wurtzite structure of InN QDs was confirmed by X-ray diffraction. The dot densities were varied by varying the indium flux. Variation of dot density was confirmed by FESEM images. Interdigitated electrodes were fabricated using standard lithography steps to form metal-semiconductor-metal (MSM) photodetector devices. The devices show strong infrared response. It was found that the samples with higher density of InN QDs showed lower dark current and higher photo current. An explanation was provided for the observations and the experimental results were validated using Silvaco Atlas device simulator.

Measurement of polar C-plane and nonpolar A-plane InN/ZnO heterojunctions band offsets by x-ray photoelectron spectroscopy

The valence band offsets of the wurtzite polar C-plane and nonpolar A-plane InN/ZnO heterojunctions are directly determined by x-ray photoelectron spectroscopy to be 1.76 +/- 0.2 eV and 2.20 +/- 0.2 eV. The heterojunctions form in the type-I straddling configuration with a conduction band offsets of 0.84 +/- 0.2 eV and 0.40 +/- 0.2 eV. The difference of valence band offsets of them mainly attributes to the spontaneous polarization effect. Our results show important face dependence for InN/ZnO heterojunctions, and the valence band offset of A-plane heterojunction is more close to the "intrinsic" valence band offset.

Impact of polarization on quasi-two-dimensional exciton and barrier-width dependence of the exciton associated transition in wurtzite III-V nitride quantum wells

Excitonic states in AlxGa1-xN/GaN quantum wells (QWs) are studied within the framework of effective-mass theory. Spontaneous and piezoelectric polarizations are included and their impact on the excitonic states and optical properties are studied. We witnessed a significant blue shift in transition energy when the barrier width decreases and we attributed this to the redistribution of the built-in electric field between well layers and barrier layers. For the exciton the binding energies, we found in narrow QWs that there exists a critical value for barrier width, which demarcates the borderline for quantum confinement effect and the quantum confined Stark effect. Exciton and free carrier radiative lifetimes are estimated by simple argumentation. The calculated results suggest that there are efficient non-radiative mechanisms in narrow barrier QWs. (C) 2002 Elsevier Science Ltd. All rights reserved.

Measurement of w-InN/h-BN Heterojunction Band Offsets by X-Ray Photoemission Spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) of the w-InN/h-BN heterojunction. We find that it is a type-II heterojunction with the VBO being -0.30 +/- A 0.09 eV and the corresponding conduction band offset (CBO) being 4.99 +/- A 0.09 eV. The accurate determination of VBO and CBO is important for designing the w-InN/h-BN-based electronic devices.

InN/GaN heterojunction electrical behavior

Indium nitride (InN) has been the subject of intense research in recent years. Some of its most attractive features are its excellent transport properties such as its small band edge electron effective mass, high electron mobilities and peak drift velocities, and high frequency transient drift velocity oscillations [1]. These suggest enormous potential applications for InN in high frequency electronic devices. But to date the high unintentional bulk electron concentration (n~1018 cm-3) of undoped InN samples and the surface electron accumulation layer make it a hard task to create a reliable metalsemiconductor Schottky barrier. Some attempts have been made to overcome this problem by means of material oxidation [2] or deposition of insulators [3]. In this work we present a way to obtain an electrical rectification behaviour by means of heterojunction growth. Due to the big band gap differences among nitride semiconductors, it’s possible to create a structure with high band offsets. In InN/GaN heterojunctions, depending on the GaN doping, the magnitude of conduction and valence band offset are critical parameters which allow distinguishing among different electrical behaviours. The earliest estimate of the valence band offset at an InN–GaN heterojunction in a wurtzite structure was measured to be ~0.85 eV [4], while the Schottky barrier heights were determined to be ~ 1,4 eV [5].We grew In-face InN layer with varying thickness (between 150 nm and 1 mm) by plasma assisted molecular beam epitaxy (PA-MBE) on GaNntemplates (GaN/Al2O3), with temperatures ranging between 300°C and 450°C. The different doping in GaN template (Si doping, Fe doping and Mg doping) results in differences in band alignments of the two semiconductors changing electrical barriers for carriers and consequently electrical conduction behaviour. The processing of the devices includes metallization of the ohmic contacts on InN and GaN, for which we used Ti/Al/Ni/Au. Whereas an ohmic contact on InN is straightforward, the main issue was the fabrication of the contact on GaN due to the very low decomposition temperature of InN. A standard ohmic contact on GaN is generally obtained by high temperature rapid thermal annealing (RTA), typically done between 500ºC and 900ºC[6]. In this case, the limitation due to the presence of In-face InN imposes an upper limit on the temperature for the thermal annealing process and ohmic contact formation of about 450°C. We will present results on the morphology of the InN layers by X-Ray diffraction and SEM, and electrical measurements, in particular current-voltage and capacitance-voltage characteristics.