InP-based Materials Research Articles

High-Responsivity InGaAs/InP Quantum-Well Infrared Photodetectors Prepared by Metal Organic Chemical Vapor Deposition

Ten-period InGaAs/InP quantum-well infrared photodetectors (QWIPs) with and without compressive strain in the quantum-well region prepared by metal organic chemical vapor deposition (MOCVD) are investigated in this study. At a detection wavelength of 8 µm, a high responsivity of 20 A/W is observed for the unstrained device, which is attributed to the higher gain of the InP-based material than that of the GaAs-based material. Compared with the unstrained QWIP, the InGaAs/InP QWIP with 1% compressive strain (CS) in the QWs has demonstrated three orders of magnitude dark current depressions so that higher peak detectivity of 2.9 ×1010 cm·Hz1/2/W at 1.3 V is observed for the device.

Optical Investigations of Directly Wafer-Bonded InP–GaAs Heterojunctions

The optical characteristics of directly wafer-bonded InP–GaAs heterojunctions have been investigated. By designing the bonding interface at standing-wave antinode, its influence on optical performances of bonded structures is magnified, which facilitates experimental detection using optical methods. Wavelength blueshift and reflectivity falling at the resonance mode were observed in wafer-bonded InP–GaAs heterostructures. Numerical analysis suggests that two effects involving thickness change of interfacial bonding layers and extra optical loss introduced by bonded junctions are responsible for the experimental observations, and these effects can be attenuated by lowering anneal temperatures and incorporating an superlattice into the surface of InP-based materials. The results are useful for designing effective optical characteristics of wafer-bonded device structures.

Al(In)As–(Ga)InAs strain-compensated active regions for injectorless quantum cascade lasers

We present a new design for quantum cascade lasers (QCLs) without the typically used injector between two consecutive active stages. The lasers are realized with the InP-based material system AlInAs/GaInAs. With additional AlAs and InAs layers a significant optimization of the structure can be realized. In this improved structure the possibility of electrons escaping into the quasi-continuum is drastically reduced by the AlAs-blocking layer. On the other hand, InAs, a material with a very low effective mass, significantly prolongs the carrier lifetime, enhancing the population inversion and increasing the dipole matrix element of the transition. Both inserted layers result in an overall improvement of the device properties, basically the threshold current density ( j th), maximum operating temperature ( T max), output power, slope efficiency and characteristic temperature T 0. With high reflection coated facets a record threshold current density as low as 450 A/cm 2 at 300 K was achieved in the pulsed mode.

Influence of proximity effects in electron-beam lithography on the optical properties of planar photonic-crystal waveguides

To measure the influence of proximity effects in electron-beam lithography on the optical properties of planar photonic crystal (PPC) waveguides we propose a PPC structure called the “PECmeter.” The PECmeter consists of nearly identical PPC waveguides which only differ in the number of rows of holes along the waveguide. The difference in the number of rows does not influence the modal properties directly but changes the diameter of the holes neighboring the waveguide through the proximity effect. The operation principle of the PECmeter is demonstrated using energy-intensity simulations of a W3 waveguide (three missing rows of holes) mini stop band. The principle is confirmed experimentally with structures fabricated in the InP-based material system and measured by the end-fire transmission technique. The results clearly show that the application of proximity-effect correction (PEC) is crucial for the fabrication of PPC waveguides. We demonstrate that when using the midpoint-equalization PEC method a near-to-perfect correction with sub-nm hole-radius uniformity can be achieved. We show the PECmeter to be sensitive enough to detect hole-radius changes as small as ΔR=0.4 nm.

Recent Progress on 1.55-$\mu{\hbox {m}}$ Dilute-Nitride Lasers

We review the recent developments in GaAs-based 1.55-mum lasers grown by molecular beam epitaxy (MBE). While materials growth is challenging, the growth window appears to be relatively broad and is described in detail. The key considerations for producing high-quality GalnNAsSb material emitting at 1.55-mum regime are examined, including the nitrogen plasma conditions, ion removal from the nitrogen flux, surfactant- mediated growth, the roles of various V-II ratios, the growth temperature, the active region thermal budget, proper annealing, and composition. We find that emission may be tuned throughout the 1.55-mum communications band without penalty to the optical quality varying only one parameter - the total growth rate. This powerful result is validated by the demonstration of low-threshold edge-emitting lasers throughout the 1.55-mum regime, including threshold current densities as low as 318 A/cm2 at 1.54 mum. Additional characterization by Z-parameter techniques, cavity length studies, and band offset measurements were performed to better understand the temperature stability of device performance. Lasing was extended as far as 1.63 mum under nonoptimized growth conditions. The GaAs-based dilute-nitrides are emerging as a very promising alternative to InP-based materials at 1.55-mum due to their high gain, greater range of achievable band offsets, as well as the availability of lattice-matched AlAs-GaAs materials and native oxide layers for vertical-cavity surface-emitting lasers (VCSELs). Indeed, this effort has enabled the first electrically injected C-band VCSEL on GaAs.

High-power, continuous-operation intersubband laser for wavelengths greater than 10μm

In this letter, high-power continuous-wave emission (>100mW) and high temperature operation (358K) at a wavelength of 10.6μm is demonstrated using an individual diode laser. This wavelength is advantageous for many medium-power applications previously reserved for the carbon dioxide laser. Improved performance was accomplished using industry-standard InP-based materials and by careful attention to design, growth, and fabrication limitations specific to long-wave infrared semiconductor lasers. The main problem areas are explored with regard to laser performance, and general steps are outlined to minimize their impact.

Fabrication and Characterization of InP-Based Quantum Cascade Distributed Feedback Lasers with Inductively Coupled Plasma Etched Lateral Gratings

We present details of the fabrication and operating characteristics of quantum cascade distributed feedback lasers with lateral gratings. These devices emit light with a wavelength of ∼10 µm and operate with pulsed drive current above room temperature. InP-based material offers significant advantages over the GaAs system for mid-infrared quantum cascade lasers. High performance, single-mode lasers are achieved using InP-based material grown by metal organic vapor phase epitaxy and utilising double-sided lateral gratings. The deeply etched gratings were made possible by the development of a high aspect ratio, multi-stage, inductively coupled plasma (ICP) etch process, using Cl2/Ar and SiCl4/Ar gas mixtures. Threshold current density was measured to be ∼5.5 kA/cm2 at a temperature of 293 K. Side mode suppression ratios >20 dB and a tuning coefficient of -0.067 cm-1 K-1 were observed.

Growth of InAs-containing quantum wells for InP-based VCSELs emitting at 2.3 μm

Vertical-cavity surface-emitting lasers are attractive light sources particularly for gas-sensing applications. Using the AlGaInAs/InP material system, an emission wavelength ranges from 1.3 to 2.05 μm has already been achieved [G. Boehm, M. Ortsiefer R. Shau, J. Rosskopf, C. Lauer, M. Maute, F. Köhler, F. Mederer, R. Meyer, M.-C. Amann, in: Proceedings of MBE XII, J. Crystal Growth (2002) pp. 748–753]. Within this range, absorption lines of gases like H 2S (1590 nm), CH 4 (1654 nm), H 2O (1877 nm) and CO 2 (2004 nm) are detectable [G. Totschnig, M. Lackner, R. Shau, M. Ortsiefer, J. Rosskopf, M.-C. Amann, F. Winter, Meas. Sci. Technol. 14 (2003) 472]. The aim of this work is a further expansion of the emission wavelength up to 2.3 μm, exploiting the well-known InP-based material system and the fabrication technique of buried tunnel junction (BTJ) VCSELs [R. Shau, M. Ortsiefer, J. Rosskopf, G. Boehm, C. Lauer, M. Maute, M.-C. Amann, in: Proceedings of SPIE, 5364 (2004) 1–15] to reach the technologically important absorption lines of carbon monoxide (CO) around 2.33 μm.

High-Speed Low-Loss Schottky-i-n InP-Based Optical Modulator for RF Photonics

An InP-based high-speed optical modulator is presented. The Schottky-i-n waveguide structure on InP-based material was used to reduce the switching voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pi</sub> and the excess loss, while maintaining high-modulation efficiencies. To minimize residual amplitude modulation and to improve power handling capability, the bulk electrooptic effect in InGaAlAs was utilized for phase shifting. As a result, a simple structure InAlAs-InGaAlAs Mach-Zehnder optical modulator with traveling-wave electrodes was fabricated and characterized. This device achieved a switching voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pi</sub> of 3.6 V, extinction ratio (>23 dB) and high-speed operation at 1.55-mum wavelength

Development and fabrication of monolithically integrated optical packet switches

&lt;p&gt;&lt;a href="http://www.osa-jon.org/virtual_issue.cfm?vid=26"&gt;Feature Issue on Photonics in Switching&lt;/a&gt;&lt;/p&gt;We report development activities towards realization of fully integrated1×2, 2×2, and 4×4 cross-point optical switches for WDM-packet-based data networking. Two enabling technologies, quantum-well intermixing and etched turning mirrors, are developed and demonstrated in InGaAs/InAlGaAs InP-based material at a wavelength of 1.55 μm. We describe the use of both technologies to fabricate switch chips with different port counts.

High performance InP-based quantum cascade distributed feedback lasers with deeply etched lateral gratings

The fabrication and operating characteristics of lateral grating distributed feedback InP-based quantum cascade lasers emitting at λ∼10μm are reported. High performance, room temperature single mode lasers, utilizing double-sided lateral gratings, are achieved in InP-based material grown by metal organic phase epitaxy. These deeply etched gratings are made possible by the development of a high aspect ratio, multistage, inductively coupled plasma etch process. A threshold current density of ∼5.5kA∕cm2 is measured at room temperature and side mode suppression ratio &amp;gt;20dB with a tuning coefficient of −0.067cm−1K−1 is observed over a temperature range of 190–330K.

An ultrafast InP/InGaAsP optical modulator

Direct-bandgap III-V semiconductor materials based on InP allow monolithic integration of optical functionality with electronic circuitry for optical communication applications. The quaternary III-V alloy, InGaAsP, is particularly important because its bandgap can be tuned to different wavelength windows by adjusting its composition, while keeping its lattice matched to InP. Optoelectronic modulators, which translate electrical pulses into light pulses, are a critical component for communications. Here we show how, by electrically inducing a 2.5mm-long Distributed Bragg Reflector in an InP/InGaAs Prib waveguide, we can theoretically realize a modulator capable of a switching speed over 40GHz. The proposed device, shown in cross section in Figure 1, is a vertical InP/InGaAsP p-i-n diode, in which the intrinsic InGaAsP layer defines the optical channel. The anode is periodically spaced along the top of waveguide, as shown in schematic top view in Figure 1. The principle of operation is straightforward. When the diode is unbiased, the device is transparent and light can travel along the modulator without being affected by loss. When a negative voltage is applied between anode and cathode, a Bragg reflector is induced, due to the periodic refractive-index variation in the intrinsic region caused by spatial periodicity of the anode along the 2.5mm waveguide. The periodic index variation causes the light to be reflected rather than transmitted. When an electric field is applied to a semiconductor, two main types of effect can induce a refractive-index variation: the first is related directly to electric field strength (electro-optic effect), while the other type includes several effects related to the change of the free-carrier concentration. In InP-based materials, no single effect is dominant. To predict grating reflectivity, it is necessary to know how the effective index of the junction varies with the applied anode bias. The first step is to compute the refractive-index variation in the Figure 1. The left panel shows a schematic cross-section of the proposed modulator, where the guiding layer is intrinsic InGaAsP. The top signal electrode (the anode) is patterned into a comb-like shape, as shown in the top view of the device on the right.

Characterization of hydrogen silsesquioxane as a Cl[sub 2]∕BCl[sub 3] inductively coupled plasma etch mask for air-clad InP-based quantum well waveguide fabrication

Air-clad InGaAsP∕InGaAs quantum well waveguides have been fabricated by inductively coupled plasma (ICP) etching using hydrogen silsesquioxane (HSQ) as an etch mask. First, HSQ has been studied for its contrast and resolution in electron beam lithography by varying e-beam exposure conditions and developer concentrations. Second, its etch resistance has been investigated in a chlorine-based ICP along with UVN30, a commercially available negative tone e-beam resist. Then, the optimum conditions for the exposure and development of HSQ for a chlorine-based ICP etching of InP-based material have been explored in terms of etch resistance. InGaAsP∕InGaAs quantum well material was patterned with HSQ by electron beam lithography. The waveguide was formed by the Cl2∕BCl3 ICP etching of InGaAsP∕InGaAs quantum well material and subsequent HCl-based wet etching of InAlAs sacrificial layer. The optical properties of the released waveguides were investigated and the initial optical measurements show low waveguide loss.

Electrooptic tuning of InP-based microphotonic Fabry-Perot filters

This paper presents the experimental results for compact (20- and 40-/spl mu/m-long) electrooptically tuned deeply etched Fabry-Perot (F-P) filters in InP-based material. Both the quantum-confined Stark effect (QCSE) and carrier-injection (C-I) effects were implemented to achieve tunability of these microcavity filters. Red and blue shifts of the transmission peaks in the order of 1 to 2 nm were observed for both effects, and the limitations on C-I due to thermal effect are clearly demonstrated and discussed. The advantages and disadvantages of both tuning mechanisms are highlighted.

Compact polarization converter in InP-based material

We present a polarization converter using one-dimensional grating principles. The device is based on slanted slots etched deeply into an InP/InGaAsP heterostructure. Almost complete polarization conversion, with a 14 dB extinction ratio, is observed for a device less than 2 microm long.

Three-dimensional calculation of propagation losses in photonic crystal waveguides

Overall losses of optical waveguides, patterned in a two-dimensional photonic crystal in InP-based material system, are determined through the calculation of propagation properties by means of a full three-dimensional finite difference time domain code. Intrinsic origins of the losses related to injection, radiation and diffraction phenomena are more specially addressed, qualitatively and quantitatively. Various configurations including thick substrate and membrane-like approaches are tested. The results, compared to the best published experiments, validate our approach as a predicting tool and give trends for the design of competitive devices.

Single step quantum well intermixing with multiple band gap control for III-V compound semiconductors

We report a quantum well intermixing technique based on Ar plasma induced damage on both GaAs- and InP-based materials with single-step multiple band gap creation across a substrate. A quantum well structure with multiplewidths serves as a sensitive tool to probe the damage created by Ar plasma. The analysis reveals that the surface defects were created up to a certain depth and propagated deeper into the material upon subsequent annealing. A simple and reliable way to obtain a controlled multiple band gap was achieved by using the spatial defect modulated intermixing. Eight band gap levels were realized across a single chip of quantum well laser structure with a linear relationship to the fraction of the open area under plasma exposure. This simple approach can be implemented at a postgrowth level to a wide range of material systems to achieve multiple band gaps, suitable for photonic integration.

Wide and continuous wavelength tuning of microcavity devices for optoelectronic applications

Ultra-widely tunable microcavity devices implemented by surface micromachining are studied. We model, fabricate, and characterize 1.55-μm vertical-resonator-based optical filters and vertical cavity surface emitting lasers (VCSELs) capable of wide, monotonic, and kink-free tuning by a single control parameter. Our devices are comprised of single or multiple horizontal air gaps in the dielectric and InP-based material system. Distributed Bragg mirrors with multiple air gaps are implemented. Due to the high refractive index contrast between air (n = 1) and InP (n = 3.17), only three periods are sufficient to guarantee a reflectivity exceeding 99.8% and offer an enormous stop-band width exceeding 500 nm. Unlike InGaAsP/InP or dielectric mirrors, they ensure short penetration depth of the optical intensity field in the mirrors and low absorption values. Stress control of the suspended membrane layers is of utmost importance for the fabrication of these devices. By controlling the stress, we are able to fabricate InP membranes that are extremely thin (357 nm thick) and at the same time flat (radius of curvature above 5 mm). Micromechanical single parametric actuation is achieved by both thermal and electrostatic actuation. Filter devices with a record tuning more than 142 nm with 3.2 V are presented.

Modal analysis and engineering on inp-based two-dimensional photonic-crystal microlasers on a si wafer

We report results on hexagonal-shaped microlasers formed from two-dimensional photonic crystals (PCs) using InP-based materials transferred and bonded onto SiO/sub 2// Si wafers. Two types of hexagonal cavities are investigated : single defect (one hole missing) cavities, so-called H1 cavities (1 /spl mu/m in diameter) and two holes missing per side H2 cavities (2 /spl mu/m in diameter). Their optical properties are analyzed using photoluminescence experiments, and plane wave method simulations have been performed for comparison. High Q modes (/spl sim/600/700) have been measured and they have been shown to enable laser effect at room temperature, under pulsed optical pumping (15% duty cycle and 25-ns pulsewidth). The study of these efficient mode characteristics gives guidance for further improvement of the operation conditions of PC lasers, such as the reduction of the threshold pumping power.

Nanoimprint technology for fabrication of three-terminal ballistic junction devices in GaInAs/InP

We present processing technology based on nanoimprint lithography (NIL) and wet etching for fabrication of GaInAs/InP three-terminal ballistic junction (TBJ) devices. To transfer sub-100 nm features into a high-mobility InP-based 2DEG material, we used SiO 2/Si stamps made with electron beam lithography and reactive ion etching. After the NIL, the resist residues are removed in oxygen plasma followed by wet etching of GaInAs/InP to define the TBJ-structures. Fabricated TBJ-devices are characterized using scanning electron microscopy and electron transport measurements. Highly non-linear electrical characteristics of the TBJ structures are demonstrated and compared with E-beam defined devices.