InGaAsP Material System Research Articles

Disorder effects in nitride semiconductors: impact on fundamental and device properties

AbstractSemiconductor structures used for fundamental or device applications most often incorporate alloy materials. In “usual” or “common” III–V alloys, based on the InGaAsP or InGaAlAs material systems, the effects of compositional disorder on the electronic properties can be treated in a perturbative approach. This is not the case in the more recent nitride-based GaInAlN alloys, where the potential changes associated with the various atoms induce strong localization effects, which cannot be described perturbatively. Since the early studies of these materials and devices, disorder effects have indeed been identified to play a major role in their properties. Although many studies have been performed on the structural characterization of materials, on intrinsic electronic localization properties, and on the impact of disorder on device operation, there are still many open questions on all these topics. Taking disorder into account also leads to unmanageable problems in simulations. As a prerequisite to address material and device simulations, a critical examination of experiments must be considered to ensure that one measures intrinsic parameters as these materials are difficult to grow with low defect densities. A specific property of nitride semiconductors that can obscure intrinsic properties is the strong spontaneous and piezoelectric fields. We outline in this review the remaining challenges faced when attempting to fully describe nitride-based material systems, taking the examples of LEDs. The objectives of a better understanding of disorder phenomena are to explain the hidden phenomena often forcing one to use ad hoc parameters, or additional poorly defined concepts, to make simulations agree with experiments. Finally, we describe a novel simulation tool based on a mathematical breakthrough to solve the Schrödinger equation in disordered potentials that facilitates 3D simulations that include alloy disorder.

Static and Dynamic Analysis of Lasing Action from Single and Coupled Photonic Crystal Nanocavity Lasers**Supported by the National Key Basic Research Special Fund/CNKBRSF of China under Grant Nos 2012CB933501, 2016YFA0301102, 2016YFB0401804 and 2016YFB0402203, the National Natural Science Foundation of China under Grant Nos 61535013, 61321063 and 61137003, the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant

The single and coupled photonic crystal nanocavity lasers are fabricated in the InGaAsP material system and their static and dynamic features are compared. The coupled-cavity lasers show a larger lasing efficiency and generate an output power higher than the single-cavity lasers, results that are consistent with the theoretical results obtained by rate equations. In dynamic regime, the single-cavity lasers produce pulses as short as 113 ps, while the coupled-cavity lasers show a significantly longer lasing duration. These results indicate that the photonic crystal laser is a promising candidate for the light source in high-speed photonic integrated circuit.

A Wavelength Tunable Optical Buffer Based on Self-Pulsation in an Active Microring Resonator

A wavelength tunable optical buffer with the ability to achieve data recovery based on self-pulsation in an active microring resonator is proposed and experimentally demonstrated. The key component in the optical buffer is the microring resonator which is implemented based on an InP–InGaAsP material system incorporating two semiconductor optical amplifiers and a phase modulator, ensuring an ultrahigh Q -factor and a tunable resonance wavelength for fast self-pulsation operating at gigahertz frequencies. An optical carrier modulated by an arbitrary pulse sequence is used to trigger the self-pulsation in the microring resonator, while its output is coupled to a fiber-optic delay line in an optoelectronic delayed feedback configuration, a recursive system for data storage. Optical buffering and data recovery at 1 Gb/s are experimentally demonstrated, which is the fastest optical buffer ever reported based on self-pulsation in a microring resonator. The proposed optical buffer can be employed to perform critical telecommunication buffer functions including writing, storage, reshaping, healing, and erasing.

A fully reconfigurable photonic integrated signal processor

Photonic signal processing has been considered a solution to overcome the inherent electronic speed limitations. Over the past few years, an impressive range of photonic integrated signal processors have been proposed, but they usually offer limited reconfigurability, a feature highly needed for the implementation of large-scale general-purpose photonic signal processors. Here, we report and experimentally demonstrate a fully reconfigurable photonic integrated signal processor based on an InP–InGaAsP material system. The proposed photonic signal processor is capable of performing reconfigurable signal processing functions including temporal integration, temporal differentiation and Hilbert transformation. The reconfigurability is achieved by controlling the injection currents to the active components of the signal processor. Our demonstration suggests great potential for chip-scale fully programmable all-optical signal processing. Scientists experimentally demonstrate a fully configurable photonic integrated signal processor based on an InP–InGaAs material system by controlling the injection currents to the active components.

Dark Count Statistics in Geiger-Mode Avalanche Photodiode Cameras for 3-D Imaging LADAR

We describe cameras incorporating focal plane arrays of Geiger-mode avalanche photodiodes (GmAPDs) that enable 3-D imaging in laser radar (LADAR) systems operating at wavelengths near 1.0 and 1.5 μm. GmAPDs based on the InGaAsP material system achieve single-photon sensitivity at every pixel of the array and are hybridized to custom CMOS ROICs providing 0.25 ns timing resolution. We present camera-level performance for photon detection efficiency and dark count rate, along with a survey of the evolution of performance for a substantial number of 32 × 32 cameras. We then describe a temporal statistical analysis of the array-level dark count behavior that distinguishes between Poissonian intrinsic dark count rate and non-Poissonian crosstalk counts. We also report the spatial analysis of crosstalk events to complement the statistical temporal analysis. Differences between cameras optimized for the two different wavelengths—1.0 and 1.5 μm—are noted, particularly with regard to crosstalk behavior.

Wide Temperature Range Operation of 25-Gb/s 1.3-μm InGaAlAs Directly Modulated Lasers

High-speed 1.3-μm directly modulated lasers (DMLs) have been developed to support sharply rising optical communications traffic. The most crucial requirement for these lasers is the ability to operate over a wide temperature range with no power-consuming electric cooler. Due to poor temperature characteristics resulting from its poor electron confinement in the multiquantum well, DMLs with InGaAsP material systems have been replaced by DMLs with InGaAlAs material systems, which have stronger electron confinement. In this paper, progress in uncooled 25-Gb/s 1.3-μm InGaAlAs DMLs is summarized. A 160-μm-long ridge-waveguide-type laser showed a lower threshold current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> of 14.9 mA at high temperatures up to 95 °C, and a small signal-frequency-response bandwidth f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> of 14 GHz was achieved at a bias current of 60 mA at 95 °C. Using this laser, clear 25-Gb/s operation was obtained at 95 °C. In addition, stable operation was achieved for up to 4000 h at 85 °C, indicating the basic applicability of the device to next-generation 25-Gb/s data communication systems. Furthermore, the developed technology was applied to a novel uncooled 25-Gb/s 1.3-μm surface-emitting laser for optical interconnects, in which a 45° mirror and a lens were integrated monolithically.

Band gap dependent thermophotovoltaic device performance using the InGaAs and InGaAsP material system

Thermophotovoltaic cells with a range of band gaps are modeled under a variety of illumination conditions, including a range of source temperatures and a variable degree of spectral control. Thus, the balance between the requirements of high power densities and high efficiencies can be investigated. The influence of elevated cell temperatures, cell cooling, Auger recombination, and series resistances have been included, and all weight the optimum band gap thermophotovoltaic cell toward higher band gaps than the ∼0.5–0.6 eV conventional optimum. The cells have been modeled using fundamental physical parameters from the InGaAs and InGaAsP material system which accurately reproduce reported device performance and allow a comparison to theoretical limits.

Numerical study on gain and optical properties of AlGaInAs, InGaNAs, and InGaAsP material systems for 1.3-μm semiconductor lasers

In reference to real devices fabricated in laboratories, the optical properties of AlGaInAs, InGaNAs, and InGaAsP semiconductor material systems for 1.3-μm semiconductor lasers are systematically studied. Simulation results show that both the AlGaInAs/InP and InGaNAs/GaAs material systems have better gain performance and smaller transparency carrier density than the InGaAsP/InP material system. For the AlGaInAs/InP material system, the characteristic temperature is improved by using compensating tensile strain in barrier. Specifically, for a 250-μm-long short-cavity AlGaInAs/InP laser, when the barrier is with a compensating tensile strain of 0.39%, the characteristic temperatures in 290–330 K and 330–350 K can be enhanced to 121.7 K and 58.9 K, respectively. For the InGaNAs/GaAs material system, simulation results suggest that the laser performance can be significantly improved when the laser is with strain-compensated GaNAs barriers.

Multimode-Interference-Coupled Ring Resonators Based on Total-Internal-Reflection Mirrors

We investigate the properties of a multimode-interference (MMI) coupled ring cavity resonator with total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA) in an InGaAsP material system. The TIR mirrors were fabricated by the self-aligned process with a loss of about 1.4 dB per mirror. The resulting free spectral range (FSR) was approximately 0.8 nm (97 GHz) near 1569 nm. The on–off ratio and the full width at half maximum (FWHM) were 8 dB and 0.152 nm, respectively, corresponding to a finesse of 5.2 and a Q factor of 10,322. Hence, such resonators can be directly integrated with other devices making possible the fabrication of compact and highly functional photonic integrated circuits.

InP-based lattice-matched InGaAsP and strain-compensated InGaAs∕InGaAs quantum well cells for thermophotovoltaic applications

Quantum well cells (QWCs) for thermophotovoltaic (TPV) applications are demonstrated in the InGaAsP material system lattice matched to the InP substrate and strain-compensated InGaAs∕InGaAs QWCs also on InP substrates. We show that lattice-matched InGaAsP QWCs are very well suited for TPV applications such as with erbia selective emitters. QWCs with the same effective band gap as a bulk control cell show a better voltage performance in both wide and erbialike emission. We demonstrate a QWC with enhanced efficiency in a narrow-band spectrum compared to a bulk heterostructure control cell with the same absorption edge. A major advantage of QWCs is that the band gap can be engineered by changing the well thickness and varying the composition to the illuminating spectrum. This is relatively straightforward in the lattice-matched InGaAsP system. This approach can be extended to longer wavelengths by using strain-compensation techniques, achieving band gaps as low as 0.62eV that cannot be achieved with lattice-matched bulk material. We show that strain-compensated QWCs have voltage performances that are at least as good as, if not better than, expected from bulk control cells.

Reactive ion etching induced damage evaluation for optoelectronic device fabrication

Reactive ion etching (RIE) processes have been evaluated in terms of material damage introduced and effect on device performance. We have evaluated the damage introduced in the InP∕InGaAsP material system, in terms of surface damage depth, by various RIE-related etching processes (based on CH4∕H2 chemistry) and we have fabricated complete Fabry-Perot laser diode devices to evaluate the effect of RIE-induced damage on device performance. Electrical, optical, and reliability performance results are presented for the laser diode devices. A comparison between the laser device performance and the related surface damage depth is presented and discussed. It has been shown that a correlation exists between RIE-induced damage and optoelectronic device performance. By carefully designing RIE-related processes, which introduce low material damage, good optoelectronic device performance can be realized coupled with high device reliability.

Total internal reflection mirror-based InGaAsP ring resonators integrated with optical amplifiers

Novel ring resonators combining very small multimode interference (MMI) couplers, low loss total internal reflection (TIR) mirrors, and a semiconductor optical amplifier in InGaAsP material system are reported for the first time. The MMI length of 113 /spl mu/m is among the shortest reported. Average TIR mirror loss is about 1.1 dB per mirror. The material platform and fabrication process used are the same used for other active and passive devices except for a deep etch step. Hence, such resonators are easily integrated with other active and passive devices. A free spectral range of approximately 2 nm is observed near 1568 nm along with an on-off ratio of 14 dB, a full-width at half-maximum of about 0.3 nm, a finesse of more than 6, and a Q-factor of more than 4900.

In situ etching of InGaAsP/InP by using HCl in an MOVPE reactor

Compositional dependence of in situ etching of InGaAsP materials on InP by using HCl was investigated. This investigation found that etching rates and their compositional dependence strongly depend on etching atmosphere. The introduction of AsH 3 to PH 3 significantly reduces etching rate. Furthermore, etching rate decreases with the compositional wavelength of InGaAsP under AsH 3 /PH 3 , while they are independent of the compositional wavelength under PH 3 . These experimental results can be qualitatively explained by the suppression of the desorption of arsenic atoms when these atoms exists in the etching atmosphere. Arsenic atoms thus play an important role in the in situ etching of the InGaAsP material system. Moreover, it was found good surface morphology for all compositional wavelengths when the etching temperature was reduced to 500 °C. This is probably due to the suppression of the additional reaction between InCl or GaCl and arsenic or phosphorous atoms by lowering etching temperature. These findings are very useful for the application of in situ etching to the practical device fabrication based on InGaAsP materials.

Influence of the electrical contact on the reliability of InP-based ridge waveguide distributed feedback semiconductor diode lasers for telecommunications applications

The design of a ridge waveguide semiconductor diode laser requires the definition of a high-quality metal contact to a p-type semiconductor that has been patterned to form the laser ridge. In the InGaAsP material system, Zn-doped, p-InGaAs is used as the contact layer. An evaporated multilayer metal stack consisting of Ti, Pt, and Au is alloyed to the InGaAs to form a stable ohmic contact with good adhesion. The alloying process is an intermixing of the Ti and As. Pt is not reactive during the alloying process and acts as a diffusion barrier. In this work, the Pt and Ti layer thicknesses were varied to improve the laser reliability. The layer thicknesses were optimized with the goal of producing a minimum stress in the laser active region. A preliminary study of completely processed lasers indicates that the laser reliability is significantly influenced by the changes to the stress induced in the device by the p-contact metal stack. Further work is required to establish the relationship between the stress in the active region of the device, and the stress contribution from the p-contact metal stack.

Direct wafer bonding of III-V compound semiconductors for free-material and free-orientation integration

This paper describes the use of direct wafer bonding technique to implement the novel concept of free-material and free-orientation integration which we propose. The technique is applied for various wafer combinations of an InGaAsP material system, and the properties of the bonded structures are studied in terms of the crystalline and electrical characterization through transmission electron microscope, X-ray diffraction, and so on. This technique's advantage for use in the fabrication of lattice-mismatched structures is confirmed by the crystalline characterization, together with its second advantage of enabling bonded structures with an orientation mismatch, is investigated. The high crystalline quality of the bonded structures with both lattice and orientation mismatches is proved, and the electrical property of the bonded interface is examined for some of them. We show a practicability in a laser fabricated on a lattice- and orientation-mismatched structure by direct bonding. The results demonstrate the remarkable feasibility of using the direct wafer bonding technique to obtain integrated structures of material- and orientation-mismatched wafers with satisfactory quality.

1.26 W CW diffraction-limited InGaAsP flared amplifierat 780 nm

Flared amplifiers fabricated with InGaAsP alloys have produced 1.26 W CW at a wavelength of 780 nm in a single-lobed, diffraction-limited far field pattern. Under quasi-CW conditions, 2.4 W of diffraction-limited power has been obtained. This represents the highest diffraction-limited power reported at 780 nm and the highest diffraction-limited power reported in the InGaAsP material system.

Integrated acoustooptic and magnetooptic devices for optical information processing

Acoustooptic (AO) Bragg interactions between guided optical waves and surface acoustic waves (SAW's) and the resulting AO Bragg cell modulators have evolved in integrated AO technology in recent years. A variety of hybrid multichannel integrated AO device modules including power and interferometric RF spectrum analyzers, space switches, tunable filters, frequency shifters and modulators, analog algebraic processors, programmable correlators and other multichannel device modules have been realized in common LiNbO/sub 3/ substrate up to 1.0/spl times/3.7 cm/sup 2/ in maximum size. The prospects for realization of their counterparts in monolithic integrated format in a common substrate of InGaAsP material system are also significantly enhanced recently. These AO device modules have shown a high degree of modularity and suggested applications in optical information processing and communications. In the meantime, the magnetooptic (MO) Bragg interactions between guided optical waves and magnetostatic waves (MSWs) in yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) waveguides have resulted in miniaturized MO Bragg cell modulators in analogy with the guided-wave AO Bragg cell modulators. Most recently the performance of such MO Bragg cell modulators has been significantly improved and the modulators have been integrated with ion-milled waveguide lenses to realize hybrid integrated MO device modules, and have been utilized to demonstrate a number of novel applications. In this paper, a review of some of these integrated AO and MO device modules and applications together with some unpublished new results are presented.

Operation of strained-layer diode laser bars at1.94 µm to 27 W QCW

Laser bars 1 cm long operating at a wavelength of 1.94 mu m have been fabricated using strained quantum wells in the InGaAsP material system lattice-matched to InP. At pulse lengths of 0.5 ms with a 5% duty cycle the laser bars demonstrated record-level peak optical powers greater than 27 W at a wavelength of 1.94 mu m. Pulses up to 5 ms in duration were demonstrated with pulse energies approaching 90 mJ. >

Monolithic semiconductor soliton transmitter

A monolithic soliton transmitter is fabricated using the PPro-II process in the InGaAsP material system by integrating an electro-absorption modulator with an extended-cavity laser. The laser cavity comprises a 700-/spl mu/m-long active region, which consists of 6 strain-compensated multiple quantum wells, a 8100-/spl mu/m-long passive buried-rib waveguide section, and a Bragg reflector with a length of 250 /spl mu/m. Mode-locking of the laser section results in 8-ps pulses at a repetition rate of 4.9 GHz. The time-bandwidth product is 0.30. Using the partially reflecting grating as one of the laser mirrors allows for integration of an electro-absorption modulator as a monolithic but extra-cavity data encoder. The modulator is fabricated by growing a 2000 A thick 1.46-/spl mu/m quaternary layer on top of the waveguiding layers. At a 4.9-Gb/s data rate, an extinction ratio of 20 dB is measured at a signal wavelength of 1565.4 nm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In situ time-resolved monitoring of PH3 induced exchange reactions on GaAs under metalorganic vapor phase epitaxy conditions

Exposure of GaAs and InGaAs to PH3 is a standard step in gas switching sequences for metalorganic vapor phase epitaxy (MOVPE) growth of heterostructures in the technologically important GaAsP, InGaP, and InGaAsP material systems. The exchange of group-V atoms was monitored in situ by reflectance anisotropy spectroscopy when GaAs is exposed to PH3. The c(4×4) reconstructed, As-terminated GaAs surface is then replaced by a P-terminated structure. At standard MOVPE growth temperatures and pressures the time constant for this reaction is of the order of 100 ms. The temperature and pressure dependence of the As by P exchange is reported, and the activation energy was determined to be 1.64 eV. It is concluded that PH3 enhances the desorption of As.