Ultrathin InP Research Articles

Role of metallic nanoparticles in the optoelectronic performance enhancement of InP ultrathin film solar cell

III-V material-based ultrathin Solar Cells (SCs) garnered a great deal of interest due to their benefits such as efficient charge transport, recycling of photons, adaptability, and material usage but suffer from low optical absorption due to thicker active material. In order to increase the optical absorption in the ultra-thin SC, metal nanoparticles (MNPs) are employed that scatter the incident light in the absorber layer resulting in higher optical absorption with the reduced requirement of active material. The role of MNPs in the efficiency improvement of InP SCs has not yet been explored. Therefore, in this paper, we have investigated the impact of plasmonic MNPs of different materials such as gold (Au), silver (Ag) and aluminium (Al) placed on the top of ITO coated 280 nm ultra-thin InP SC with FDTD simulations, which employ the surface plasmon resonance (SPR) to increase the optical absorption by tuning the dimensions of the MNPs. The thickness of InP thin-film and an anti-reflective coating of ITO are optimized to achieve maximum absorption. In addition, the diameter and period of Au, Ag, and Al MNPs are also optimized to achieve higher optical Jsc, and results show that Au nanoparticle with diameter of 50 nm and period of 100 nm shows higher Jsc when compared to Ag and Al nanoparticles of optimized diameter. The device analysis shows the Au nanoparticles placed on the top surface of ITO coated InP ultrathin SC with a power conversion efficiency (PCE) of 22.3% outperform the Ag NPs and Al NPs ITO coated InP ultrathin SC and ITO/InP ultrathin SC without MNPs.

Long-Term Stability and Optoelectronic Performance Enhancement of InAsP Nanowires with an Ultrathin InP Passivation Layer.

The influence of nanowire (NW) surface states increases rapidly with the reduction of diameter and hence severely degrades the optoelectronic performance of narrow-diameter NWs. Surface passivation is therefore critical, but it is challenging to achieve long-term effective passivation without significantly affecting other qualities. Here, we demonstrate that an ultrathin InP passivation layer of 2–3 nm can effectively solve these challenges. For InAsP nanowires with small diameters of 30–40 nm, the ultrathin passivation layer reduces the surface recombination velocity by at least 70% and increases the charge carrier lifetime by a factor of 3. These improvements are maintained even after storing the samples in ambient atmosphere for over 3 years. This passivation also greatly improves the performance thermal tolerance of these thin NWs and extends their operating temperature from <150 K to room temperature. This study provides a new route toward high-performance room-temperature narrow-diameter NW devices with long-term stability.

Si microring resonator optical switch based on optical phase shifter with ultrathin-InP/Si hybrid metal-oxide-semiconductor capacitor.

We propose a microring resonator (MRR) optical switch based on III-V/Si hybrid metal-oxide-semiconductor (MOS) optical phase shifter with an ultrathin InP membrane. By reducing the thickness of the InP membrane, we can reduce the insertion loss of the phase shifter, resulting in a high-quality-factor (Q-factor) MRR switch. By optimizing the device structure using numerical analysis, we successfully demonstrated a proof-of-concept MRR optical switch. The optical switch exhibits 0.3 pW power consumption for switching, applicable to power-efficient, thermal-crosstalk-free, Si programmable photonic integrated circuits (PICs) based on wavelength division multiplexing (WDM).

Taperless Si hybrid optical phase shifter based on a metal-oxide-semiconductor capacitor using an ultrathin InP membrane.

We propose a III-V/Si hybrid metal-oxide-semiconductor (MOS) optical phase shifter using an ultrathin InP membrane, which allows us to eliminate the III-V taper required for mode conversion between Si and hybrid waveguides. We numerically revealed that thinning a III-V membrane can reduce the insertion loss of the phase shifter while maintaining high modulation efficiency because the optical phase shift is induced by carrier accumulation at the MOS interface. We experimentally demonstrated the proposed optical phase shifter with an ultrathin InP membrane and achieved the modulation efficiency of 0.54 Vcm and the insertion loss of 0.055 dB. Since the taperless structure makes the hybrid integration easier and more flexible, the hybrid MOS optical phase shifter with an ultrathin III-V membrane is promising for large-scale Si programmable photonic integrated circuits.

Ultrathin InP annular nanohole arrays for efficient light absorption solar cells

This Letter proposes ultrathin InP films consisting of annular nanohole arrays (ANAs) for highly efficient solar cells. By tailoring the inner and outer radii of ANAs properly and combining antireflection coating (ZnO) and back-reflector (Ag), the photocurrent generated in the InP based dielectric-semiconductor-metal (DSM) configuration can be increased dramatically by 124.6% with respect to the planar solar cell of equal geometric thickness (100 nm). The fact that the DSM-ANA structure is able to harvest broadband and wide-angle incident light can be attributed to the excitation of leaky waveguide modes, Bloch modes, and surface plasmon polariton modes. This work provides a promising and feasible way to design and fabricate efficient ultrathin InP photovoltaic and other optoelectronic devices.

Reliability of Passivated and Unpassivated High-k Dielectric/GaAs Metal-Oxide-Semiconductor Capacitors

Metal-oxide-semiconductor (MOS) capacitors were fabricated using zirconium dioxide as a high-k dielectric layer on p-GaAs substrates with and without passivation layers. Ultrathin (1.8 nm) InP and ZnO were used as a passivation layer to prevent Fermi level pinning and regrowth of GaAs-native oxides at the interface between GaAs and ZrO2. The trapping of charge carriers and device reliability were investigated in passivated and unpassivated GaAs MOS capacitors during electrical stress. The improved characteristics in terms of stress-induced interface trap variation, hysteresis voltage, stress induced leakage current, and flat-band voltage have been demonstrated in InP and ZnO passivated MOS devices. Time dependent dielectric breakdown properties were studied in presence of electrical stress. The breakdown time was found to be 1748 and 1703 s in InP and ZnO passivated devices, respectively, however, in unpassivated devices, it was 928 s. The InP passivated GaAs MOS devices show improved electrical and breakdown characteristics over other MOS devices.

Strong surface passivation of GaAs nanowires with ultrathin InP and GaP capping layers

We demonstrate efficient surface passivation of GaAs nanowires using ultrathin in-situ grown epitaxial InP and GaP capping layers, with metallo-organic vapor phase epitaxy as the growth system. The passivation increased photoluminescence intensity by three orders of magnitude compared to unpassivated nanowires, and the effect remained strong after a month of storage in air. Effective passivation was acquired over a wide range of growth temperatures, although the highest studied temperatures caused additional detrimental effects such as etching and GaAsP formation. The capping layer thickness was in the order of few monolayers. Therefore, the impact on any other properties of the nanowires besides the surface states was minuscule. As a simple and effective method the studied capping layers offer an excellent way for nanowire passivation.

Selective MOVPE growth of GaInAs/InP MQW on directly‐bonded InP/Si substrate

AbstractAn ultrathin InP template with extremely low defect density was realized on Si substrate using wet etching and wafer direct bonding technique. On top of the InP/Si substrate, asymmetric SiO2 mask pattern on one side of the arrayed waveguides was prepared and selective metal‐organic vapor‐phase epitaxy (MOVPE) growth has been demonstrated. According to the cross‐sectional scanning electron micrograph (SEM) images, gradually varied height of GaInAs/InP multiple quantum well (MQW) structures were realized on the substrate and photo‐luminescence (PL) measurement showed different band‐gaps of the MQW structures. Our approach is of importance to control the in‐plane band‐gap energy for the integration of InP‐based various functional devices on Si substrate. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

GaAs metal-oxide-semiconductor based nonvolatile memory devices embedded with ZnO quantum dots

Ultrathin InP passivated GaAs non-volatile memory devices were fabricated with chemically synthesized 5 nm ZnO quantum dots embedded into ZrO2 high-k oxide matrix deposited through metal organic chemical vapor deposition. In these memory devices, the memory window was found to be 6.10 V and the obtained charge loss was only 15.20% after 105 s. The superior retention characteristics and a wide memory window are achieved due to presence of ZnO quantum dots between tunneling and control oxide layers. Room temperature Coulomb blockade effect was found in these devices and it was ascertained to be the main reason for low leakage. Electronic band diagram with program and erase operations were described on the basis of electrical characterizations.

Extremely improved InP template and GaInAsP system growth on directly‐bonded InP/SiO2‐Si and InP/glass substrate

AbstractWe have developed an ultrathin InP template with low defect density on SiO2‐Si and glass substrate by employing wet etching and wafer direct bonding technique. We have demonstrated epitaxial growth on these substrates and GaInAs/InP multiple quantum well layers were grown by low pressure metal‐organic vapor‐phase epitaxy. Photoluminescence measurements of the layers show that they are optically active and we have obtained almost the same intensity from these substrates compared to the InP substrate. These results may be attributed to improvement of InP template quality and should provide further improvements in device performance realized on SiO2‐Si and glass substrate. And, these are promising results in terms of integration of InP‐based several functional optical devices on SiO2‐Si and glass substrate. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Role of ultra thin pseudomorphic InP layer to improve the high-k dielectric/GaAs interface in realizing metal-oxide-semiconductor capacitor

In this article, we report GaAs metal-oxide-semiconductor (MOS) capacitors with a metal organic chemical vapor deposited ultrathin (1.5 nm) pseudomorphic InP interface passivation layer (IPL) and a thin (5 nm) ZrO2 high-k dielectric. Reduction of the surface states on InP passivated GaAs surfaces was observed from the photoluminescence study. The x-ray photoelectron spectra confirmed the dramatic reduction of GaAs native oxides (Ga-O and As-O) from the interface of ZrO2 and p-GaAs, implying that the Fermi level at the high-k/GaAs interface can be unpinned with good interface quality. As a result, very low values of interface trap density (1.1 × 1011 cm−2 eV−1) and hysteresis (8.21 mV) were observed. The same was done for directly deposited ZrO2 on GaAs surface to understand the efficacy of InP interface passivation layer on GaAs MOS devices. A systematic capacitance-voltage and current density-voltage studies were performed on bothAl/ZrO2/InP/p-GaAs and Al/ZrO2/p-GaAs structures. It was found that insertion of 1.5 nm InP ultrathin layer in-between ZrO2 and GaAs improves the essential parameters of GaAs MOS such as dielectric constant, frequency dispersion, leakage current, etc. The dielectric reliability has been studied with constant voltage stressing. A very small flatband voltage shift with stress time was observed in InP passivated GaAs MOS capacitors.

Growth and surface passivation of near-surface InGaAs quantum wells on GaAs (1 1 0)

The growth and surface passivation of near-surface InGaAs quantum wells (QWs) on GaAs (1 1 0) substrate have been investigated. Triangular shaped small islands, approximate areal density of 10 7 cm - 2 , are observed on metal organic vapor phase epitaxially grown GaAs single layer and InGaAs multi-quantum wells (MQWs) surfaces in a wide range of growth temperatures. By optimizing the growth conditions, high quality In 0.22 Ga 0.78 As QWs with optical properties comparable to the same structure grown on GaAs (1 0 0) are obtained. Near-surface single QWs are used to study the surface passivation. Epitaxially in situ grown mono-layer thick GaP and InP layers as well as surface phosphorization with tertiarybutylphosphine (TBP) are utilized as passivation methods. Passivation significantly increases photoluminescence (PL) intensity and carrier lifetime of near-surface QWs. The best passivation efficiency is obtained by surface phosphorization with TBP on (1 1 0)-oriented near-surface QW while the ultra-thin InP layer is the best on (1 0 0)-oriented near-surface QW. After 7 months of air exposure, all passivated near-surface QWs still show high PL intensity comparable to deep QW while the PL intensity of unpassivated samples degraded severely. Also, the differences between the optical properties of QWs on GaAs (1 1 0) and (1 0 0) substrates are observed and discussed.

InP monolayers inserted in a GaP matrix studied by spectroscopic ellipsometry

Ellipsometric measurements on single ultrathin InP layers of 0.5 and 1 monolayer (ML) thickness inserted into GaP by metal-organic vapor phase epitaxy (MOVPE) growth have been carried out at room temperature in the blue spectral range (hv = 2.5 to 2.9eV) around the GaP direct gap. Due to the insertion of the InP monolayers, the optical dielectric function of the GaP host material is strongly modified in dependence on the InP layer thickness.

Enhanced optical properties of in situ passivated near-surface AlxGa1−xAs/GaAs quantum wells

An epitaxial method for in situ passivation of epitaxial AlxGa1−xAs/GaAs surfaces is reported. The deposition of an ultrathin InP layer (about one monolayer) on the surface of AlxGa1−xAs/GaAs structures by metalorganic vapor phase epitaxy results in drastically reduced surface recombination. The effect is studied by low-temperature photoluminescence of near-surface Al0.22Ga0.78As/GaAs quantum wells where the top barrier thickness is varied from 0 to 50 nm. At the thicknesses of ≤5 nm, the intensity from passivated samples is more than four orders of magnitude larger than that obtained from unpassivated structures. For a passivated surface quantum well where InP is deposited directly onto the GaAs quantum well, we observe a blueshift of 15 meV and an intensity reduction of only a factor of 10 as compared to the luminescence from a quantum well placed at a depth of 50 nm from the surface.

Migration and related buried epitaxy using digital epitaxial growth conditions

Selective or buried epitaxy was demonstrated on grooved or mesa substrates by the digital epitaxy by which fine thickness control of ultra-thin GaInAs or InP at atomic scale has been achieved in the wider space ranges of epitaxial layers. The migration of the group III source plays an important role both in maskless selective epitaxy and in maskless buried epitaxy. The migration length of TMIn and related materials as group III atoms landing on the InP (100) substrate were estimated experimentally to be 0.40 μm at a growth temperature of T g = 500°C.