Anthony J. Springthorpe

What limits the maximum output power of long-wavelength AlGaInAs/InP laser diodes?

We analyze the high-temperature continuous-wave performance of 1.3-/spl mu/m AlGaInAs/InP laser diodes grown by digital alloy molecular-beam epitaxy. Commercial laser software is utilized that self-consistently combines quantum-well bandstructure and gain calculations with two-dimensional simulations of carrier transport, wave guiding, and heat flow. Excellent agreement between simulation and measurements is obtained by careful adjustment of material parameters in the model. Joule heating is shown to be the main heat source; quantum-well recombination heat is almost compensated for by Thomson cooling. Auger recombination is the main carrier loss mechanism at lower injection current. Vertical electron escape into the p-doped InP cladding dominates at higher current and causes the thermal power roll-off. Self-heating and optical gain reduction are the triggering mechanisms behind the leakage escalation. Laser design variation is shown to allow for a significant increase in the maximum output power at high temperatures.

Short-wavelength laser diodes based on AlInAs/AlGaAs self-assembled quantum dots

Self-assembled quantum dots (QDs) of highly strained InAlAs have been grown by molecular beam epitaxy in separate-confinement p–i–n heterostructures on (001) GaAs substrates. Results from a systematic study of samples with varying amounts of deposited material relates the observed emission peaks with QD levels, wetting layer states, or barrier materials. For samples with high-QD concentration, lasing is observed in the upper-QD shells. A sample with contact layers improving carrier and optical confinement operates up to room temperature and displays lowered threshold current densities. A threshold current density of ∼4 A/cm2 is measured for this structure at T=5 K and continuous-wave operation is obtained up to T∼77 K. A material gain larger than 1.7×104 cm−1 is measured for this single-layer structure. Lasing is observed in the upper-QD shells for small gain media, and progresses towards the QD lower states for longer cavity lengths representing an emission shift of 45 meV. A minor dependence of the thre...

Self-timed integrated-optical serial-to-parallel converter for 100 Gbit/s time demultiplexing

We describe a novel all-optical serial-to-parallel (S/P) converter using surface-emitted second harmonic generation (SHG). This passive self-timing integrated-optical device is designed to demultiplex optical signals at rates exceeding 100 Gb/s. The results of a proof-of-concept demonstration are presented.<<ETX>>

Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-/spl mu/m AlGaInAs MQW lasers

The potential of 1.3-/spl mu/m AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20/spl deg/C-100/spl deg/C temperature range indicate a localized T/sub 0/ value of 68 K at 98/spl deg/C for a device with a 2.8 /spl mu/m ridge width and 700-/spl mu/m cavity length. The transparency current density is measured for temperatures from 20/spl deg/C to 60/spl deg/C and found to increase at a rate of 7.7 A/spl middot/cm/sup -2//spl middot/ /spl deg/C/sup -1/. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3/spl times/10/sup -4/ A/sup -1//spl middot//spl deg/C/sup -1/. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular ( A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20/spl deg/C-80/spl deg/C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems.

Calibrated scanning spreading resistance microscopy profiling of carriers in III–V structures

Two-dimensional carrier profiling using scanning spreading resistance microscopy (SSRM) has recently been reported for Si- and InP-based structures. In this article, we report SSRM measurements solely on III–V material-based structures. We have studied GaAs and InP doping staircase structures, prepared using molecular-beam epitaxy. These structures were then used as calibration standards for the profiling of carrier density in state-of-the-art III–V-based optoelectronic devices. We discovered that SSRM data on GaAs can be obtained with either polarity; however, only one polarity (positive or negative sample bias for n- or p-GaAs, respectively) produces SSRM results that show quantitative correlation with dopant concentration as determined by secondary ion mass spectrometry (SIMS). In comparison, SSRM measurements using both bias polarities on n-InP correlates well with SIMS, while p-InP exhibits a similar polarity dependence to p-type GaAs. A physical model based on a Schottky junction is proposed to expl...

Integrated piezoresistive sensors for atomic force-guided scanning Hall probe microscopy

We report the development of an advanced sensor for atomic force-guided scanning Hall probe microscopy whereby both a high mobility heterostructure Hall effect magnetic sensor and an n-Al0.4Ga0.6As piezoresistive displacement sensor have been integrated in a single III–V semiconductor cantilever. This allows simple operation in high-vacuum/variable-temperature environments and enables very high magnetic and topographic resolution to be achieved simultaneously. Scans of magnetic induction and topography of a number of samples are presented to illustrate the sensor performance at 300 and 77 K.

Micromachined III–V cantilevers for AFM-tracking scanning Hall probe microscopy

In this paper we report the development of a new III–V cantilever-based atomic force sensor with piezoresistive detection and an integrated Hall probe for scanning Hall probe microscopy. We give detailed descriptions of the fabrication process and characterization of the new integrated sensor, which will allow the investigation of magnetic samples with no sample preparation at both room and cryogenic temperatures. We also introduce a novel piezoresistive material based on the ternary alloy n+-Al0.4Ga0.6As which allows us to achieve a cantilever deflection sensitivity ΔR/(R Δz) = 2 × 10−6 A−1 at room temperature.

Two-photon absorption-induced self-phase modulation in GaAs-AlGaAs waveguides for surface-emitted second-harmonic generation.

Performance-limiting asymmetric distortion is observed in the spectra of fundamental pulses transmitted through GaAs-Al(0.9)Ga(0.1)As multilayer waveguides designed for surface-emitted second-harmonic generation. This behavior is attributed to refractive-index changes resulting from the accumulation of free carriers created by two-photon absorption in the GaAs layers. Numerical simulations of the intensity-dependent spectra by use of the separately measured two-photon absorption coefficient are shown to be in good agreement with the observed spectra.

Direct imaging of the depletion region of an InP p-n junction under bias using scanning voltage microscopy

We directly image an InP p–n junction depletion region under both forward and reverse bias using scanning voltage microscopy (SVM), a scanning probe microscopy (SPM) technique. The SVM results are compared to those obtained with scanning spreading resistance microscopy (SSRM) measurements under zero bias on the same sample. The SVM and SSRM data are shown to agree with the results of semiclassical calculations. The physical basis of the SVM measurement process is also discussed, and we show that the measured voltage is determined by the changes in the electrostatic potential and the carrier concentration at the SVM tip with and without the applied bias.

Compositional control in molecular beam epitaxy growth of GaNyAs1−y on GaAs (001) using an Ar/N2 RF plasma

Abstract Single and multiple quantum wells of GaN y As 1− y were grown on GaAs substrates using solid-source molecular beam epitaxy (MBE) with an RF plasma cell. Dynamic gas switching was used to control the gas composition and active nitrogen flux produced using ultra-pure Ar/N 2 gas mixtures. Real-time optical spectroscopy of the plasma during growth was used to monitor the active nitrogen flux and to optimize the growth method. High-resolution X-ray diffraction, secondary ion mass spectrometry, transmission electron microscopy and low temperature photoluminescence spectroscopy were used to study the composition, structural and optical quality of the structures. We demonstrate the exceptional sensitivity of these techniques to the nitrogen profiles in the films and the high quality of the layers produced using the Ar dilution technique.