Quantum Well Intermixing Research Articles

Wavelength monitoring with low-contrast multimode interference waveguide

We demonstrate a wavelength monitor based on interference effect in planar quantum-well waveguide fabricated using argon plasma quantum-well intermixing. The passive device exhibits a characteristic curve, which is used to determine the wavelength of an arbitrary input light near the 1550-nm window. It has an exponential-like wavelength response in the wavelength range 1520-1620 nm and resolution of 0.2 nm.

Plasma-induced quantum well intermixing for monolithic photonic integration

Plasma-induced quantum well intermixing (QWI) has been developed for tuning the bandgap of III-V compound semiconductor materials using an inductively coupled plasma system at the postgrowth level. In this paper, we present the capability of the technique for a high-density photonic integration process, which offers three aspects of investigation: 1) universality to a wide range of III-V compound material systems covering the wavelength range from 700 to 1600 nm; 2) spatial resolution of the process; and 3) single-step multiple bandgap creation. To verify the monolithic integration capability, a simple photonic integrated chip has been fabricated using Ar plasma-induced QWI in the form of a two-section extended cavity laser diode, where an active laser is integrated with an intermixed low-loss waveguide.

Monolithically integrated active components: a quantum-well intermixing approach

As the demand for bandwidth increases, the communications industry is faced with a paradigm shift. Photonic integration is a key technology that will facilitate this shift. Monolithic integration allows for the realization of highly functional optical components, called photonic integrated circuits. Herein, we discuss the advantages and potential applications of photonic integration, and after a brief overview of various integration techniques, provide a detailed look at our work using a novel quantum well intermixing processing platform.

Photocurrent spectroscopy analysis of widely tunable negative-chirp quantum-well intermixed laser-modulator transmitters

High-speed laser-modulator transmitters fabricated using InGaAsP quantum-well intermixing exhibit negative chirp over a wavelength range of more than 30nm. Photocurrent spectroscopy is used to examine the multiple band edges in these devices. An exciton peak is found in the photocurrent data, and the evolution of the band edge as a function of quantum-well intermixing and applied bias voltage is revealed. The photocurrent data are then exploited to verify and explain the negative chirp characteristics of the wavelength-agile transmitters.

Quantum-well Intermixing using Ge-doped Sol-gel Derived Silica Encapsulant Layer

ABSTRACTWe report the intermixing enhancement using the Ge-doped sol-gel derived silica encapsulant layer in InGaAs/InGaAsP quantum-well laser structure. A bandgap shift of ∼64 nm has been observed from 16% Ge-doped silica capped sample at an annealing temperature of 630°C while the intermixing at the similar temperature can be effectively suppressed with the e-beam evaporated SiO2 encapsulant layer. Using our theoretical model, nearly identical activation energy of 1.7±0.5 eV was obtained from the intermixed sample with Ge-doped silica. Similar intermixing enhancement holds for high Ge-content cap in the intermixed GaAs/AlGaAs quantum-wells related to Ga vacancy injection. We postulate that the dissimilarity in interdiffusion behavior between 0% and 16% Ge-doped silica capped sample is only attributed to the difference in the number of beneficial vacancies that involve in the intermixing process.

Widely tunable negative-chirp SG-DBR laser/EA-modulated transmitter

Ten Gb/s low power penalty (<0.5 dB) error-free transmission was achieved through 75 km using a high-performance sampled-grating (SG) distributed Bragg reflector (DBR) laser/EAM transmitter. Large signal chirp measurements show negative chirp operation across the entire tuning range of the devices. An integration-oriented quantum-well-intermixing (QWI) process was employed for the realization of these devices.

InGaAs/InGaAsP Quantum-Well Engineering for Multiple Regrowth MOVPE Process

ABSTRACTFor the heterogeneous integration of several layer structures for absorber, gain and passive waveguide sections in a monolithically-integrated mode locked laser diode, the bandgap of the absorber section has to be matched to the emission wavelength of the gain section. Because of the use of a multiple regrowth process for optical butt-coupling, the first grown multiple quantum-well gain material undergoes a quantum-well intermixing process, resulting in a blue shift of the emitting optical wavelength. Experimental results show, that the blue shift is dependent on the process details and cannot be investigated by simple thermal cycling of unprocessed quantum well-structures. With the introduction of an effective quantum-well width computed from the emission wavelength we found a linear relationship between the effective quantum well width shrinkage and the cumulated regrowth heating time of 8.3Å/h at a growth temperature of 630°C. Therefore knowing the cumulated regrowth time for a laser fabrication, we could successfully design the initial quantum well thickness that yields the targeted emitting wavelength and excellent matching to the absorber bandedge.

Improvement in spatial resolution of plasma-enhanced quantum-well intermixing by stress-inducing dielectric mask

We report the use of a stress-inducing dielectric mask to improve the spatial resolution of the proximity quantum-well intermixing process. Photoluminescence and Raman spectroscopy were used to study the band gap modification and the spatial resolution using Ar plasma in the InGaAs∕InGaAsP laser structure. A spatial resolution of 2.4μm has been achieved with the presence of an SixNy annealing cap as a stress-inducing mask. The simple technique provides a promising approach of lateral band gap tuning with a high spatial resolution for high-density photonic integrated circuits.

Reduction of Absorption Loss in Asymmetric Twin Waveguide Laser Tapers Using Argon Plasma-Enhanced Quantum-Well Intermixing

Lasers based on asymmetric twin waveguide integration technology are limited by the necessity of pumping the tapers to avoid absorption losses within this section of the active region. Here, we demonstrate that the threshold current is reduced by argon plasma-enhanced quantum-well intermixing in the taper. Intermixing induces a (57/spl plusmn/5) nm wavelength blue shift in the emission peak, accompanied by a <12-nm linewidth broadening of the photoluminescence spectrum, indicating minimal material degradation. The threshold current of a 0.6-mm-long laser is reduced by (18/spl plusmn/1)% to (27/spl plusmn/1) mA using an intermixed taper as compared to a nonintermixed structure.

Effects of proton irradiations on GaN‐based materials

We present the effects of proton irradiations on n-GaN and InGaN/GaN light emitting diodes (LEDs) investigated by secondary ion mass spectrometry (SIMS), circular transmission line model (CTLM), Raman and photoluminescence (PL) measurements. The SIMS results show that the depth of proton implantation is nearly proportional to the energy of the hot protons. Proton implantation can result in the quenching in the luminescence and the degradation in the conductivity of n-GaN, which were found to be preserved to the temperature for device processing of 750 °C. It was found that the intermixing of quantum wells (QWs) induced by proton radiations is negligible, and it is interesting to point out that InGaN/GaN QWs are more resistant to proton irradiations compared with the conventional III–V semiconductor QWs. Our results demonstrate the application of proton irradiations to the technology of electrical and optical isolation for the fabrications of compound semiconductor devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Demonstration of Widely Tunable Single-Chip 10-Gb/s Laser–Modulators Using Multiple-Bandgap InGaAsP Quantum-Well Intermixing

High-speed wavelength-agile laser-modulators were fabricated for the first time using a quantum-well intermixing processing platform for monolithic integration. Over 19-GHz 3-dB modulator bandwidth was achieved and 10-Gb/s error-free transmission was demonstrated through 75 km of standard fiber.

Barrier-enhanced InGaAs/InAlAs photodetectors using quantum-well intermixing

In this work, we model and simulate the performance of a novel InGaAs/InAlAs quantum-well metal–semiconductor–metal (MSM) photodetector at 1550-nm wavelength that utilizes recessed electrodes to access the two-dimensional (2D) transport channel. Unfortunately, rather low Schottky barrier heights on undoped InGaAs lead to excessive dark currents when metal electrodes are in direct contact with this material. To remedy this situation, we propose to form barrier-enhancement regions between the optically active 2D-quantum well and the lateral 3D-metal contacts by means of ion-implantation-induced quantum-well intermixing. Simulation results indicate a reduction in dark current of nearly three orders of magnitude. Additionally, the high-speed performance appears not to be adversely affected under normal operating conditions by the potentially deleterious effects of carrier emission and accumulation at these contact heterointerfaces. The Fourier transform of a simulated transient current response to a light impulse indicates electrical 3-dB bandwidth exceeds 50 GHz in a device with a recessed electrode gap of 1 μm.

Laser-induced selective area tuning of GaAs/AlGaAs quantum well microstructures for two-color IR detector operation

Selective area laser annealing of GaAs/AlxGa1−xAs quantum well infrared photodetector (QWIP) material has been investigated as a possible route towards the fabrication of two-color low-cost focal plane array devices. Tuning of the wavelength response of the material has been achieved as a consequence of the quantum well intermixing (QWI) effect. A 90 s irradiation with a continuous wave Nd:yttrium–aluminum–garnet laser, at the peak temperature of 850 °C, resulted in the 40 nm blueshift of the QW photoluminescence peak from 832 to 792 nm. This corresponded to the 0.7 μm redshift of the wavelength response of the investigated QWIP microstructure in the 8 μm optical absorption region. The amplitude of this shift is consistent with the literature data obtained for similar material processed directly by rapid thermal annealing (RTA) or by a two-step process involving particle implantation and RTA. We have examined the laser-QWI approach for direct writing of arrays of a two-band gap material. The preliminary results indicate the feasibility of this approach for fabricating linear arrays with a period of 0.8 mm.

Multiple-wavelength integration in InGaAs-InGaAsP structures using pulsed laser irradiation-induced quantum-well intermixing

In this paper, we present the characteristics of a quantum-well intermixing technique using pulsed-photoabsorption-induced disordering. Photoluminescence, micro-Raman spectroscopy, and transmission electron microscopy were used to characterize the process. Using this technique, a differential wavelength shift between the intermixed and nonintermixed regions of over 160 nm has been observed from InGaAs-InGaAsP heterostructures. It was found from the micro-Raman measurements that a spatial resolution of better than 2.5 /spl mu/m can be achieved. A theoretical model has been developed to estimate the spatial resolution limit. Theoretical analysis has also been performed to investigate the effect of laser irradiation on the degree of intermixing in InGaAs-InGaAsP structures. To verify the capability of this process in monolithic photonic integration, high-quality bandgap tuned lasers, two-section extended cavity lasers, and multiple-wavelength laser chips have been fabricated.

Enhancement of the Spectral Width of High-Power1.5 μm Integrated Superluminescent Light Source by Quantum WellIntermixing Process

A novel type of integrated InGaAsP superluminescent light source wasfabricated based on the tilted ridge-waveguide structure withselective-area quantum well (QW) intermixing. The bandgap structurealong the length of the device was modified by impurity free vacancydiffusion QW intermixing. The spectral width was broadened from the 16 nm ofthe normal devices to 37 nm of the QW intermixing enhanced devices at the sameoutput power level. High superluminescent power (210 mW) was obtainedunder pulsed conditions with a spectral width of 37 nm.

Quantum well intermixing for the fabrication of InGaAsN/GaAs lasers with pulsed anodic oxidation

Quantum well (QW) intermixing was carried out by post-growth rapid thermal annealing in InGaAsN/GaAs QW laser structures grown by solid-source molecular-beam epitaxy. The intensity and width of the photoluminescence peak showed a dependence on annealing temperature and time, and the maximum intensity and minimum linewidth were obtained after the wafer was annealed at 670 °C for 60 s. The peak luminescence energy blueshifted with increasing annealing time, although it plateaued at an annealing time that corresponded to that yielding the maximum luminescence intensity. The diffusion coefficient for indium was determined from a comparison between experimental data and modeling, but showed that QW intermixing alone was not sufficient to account for the relatively large blueshift after annealing. Defects related to the incorporation of nitrogen in the QW layer were responsible for the low photoluminescence efficiency in the as-grown samples and were annealed out during rapid thermal annealing. During annealing, nitrogen interstitials moved to vacancy sites within the QW and thus suppressed QW intermixing. After annealing wafers under conditions giving the maximum luminescence intensity, lasers were fabricated with pulsed anodic oxidation.

Passive Mode Locking of InAlGaAs 1.3-&amp;gt;tex&amp;lt;$muhboxm$&amp;gt;/tex&amp;lt;Strained Quantum Wells Extended Cavity Laser Fabricated by Quantum-Well Intermixing

We demonstrate continuous-wave operation and passive mode locking of extended cavity lasers fabricated in 1.3-μm InAlGaAs strained multiple quantum-wells structure. Modal losses were measured for the passive section fabricated by quantum-well intermixing. Pulse duration of 1.7 ps was deduced from intensity autocorrelation measurement.

Experimental and Theoretical Analysis of Argon Plasma-Enhanced Quantum-Well Intermixing

Plasma-enhanced quantum-well intermixing (QWI) has been developed for tuning the bandgap of InGaAs-InP material using an inductively coupled plasma system. The application of inductively coupled plasma enhances the interdiffusion of point defects resulting in a higher degree of intermixing. Based on a semi-empirical model of QW interdiffusion, the bandgap blue-shift with respect to the plasma exposure time and inductively coupled plasma energy has been analyzed. The theoretical results appear to be in good agreement with the experimental data of the intermixed samples. The model serves as a good simulation tool to explain the intermixing mechanism and further to optimize the intermixing process for the fabrication of the photonic integrated circuits.

Influence of semiconductor cap layer on the impurity-free vacancy disordering of the In0.2Ga0.8As/GaAs multiquantum-well structure by dielectric capping layers

The feasibility of normal GaAs, low-temperature-grown GaAs (LT-GaAs) and low-temperature-grown InGaAs (LT-InGaAs) as the capping layers for impurity-free vacancy disordering (IFVD) of the In0.2Ga0.8As/GaAs multiquantum-well (MQW) structure has been studied. The normal GaAs, LT-GaAs and LT-InGaAs layers were tested as the outermost capping layer and the intermediate cap layer underneath the SiO2 or Si3N4 capping layer. The degree of quantum-well intermixing (QWI) induced by rapid thermal annealing was estimated by the shift of the photoluminescence (PL) peak energy. It was found that the IFVD of the In0.2Ga0.8As/GaAs MQW structure using LT-GaAs (LT-InGaAs) as the outermost capping layer was much smaller (larger) than that using a SiO2 (Si3N4) capping layer. It was also observed that the insertion of the normal GaAs, LT-GaAs and LT-InGaAs cap layers below the SiO2 or Si3N4 capping layer reduces the degree of QWI and the PL intensity after the QWI. A plausible explanation for the influence of normal GaAs, LT-GaAs and LT-InGaAs cap layers for the QWI of the InGaAs/GaAs structure is also discussed.

Integration of high-gain and high-saturation-power active regions using quantum-well intermixing and offset-quantum-well regrowth

A novel structure and method for fabricating regions of high and low modal gain on the same chip are reported, which enable diode lasers with maximum efficiency to be monolithically integrated with multiple-section semiconductor optical amplifiers having both high gain and high saturation power. This method uses quantum-well intermixing and an offset-quantum-well regrowth to achieve regions with high and low optical confinement. Fabry-Perot broad-area lasers were used to characterise the material in both regions.