InGaAsP Quantum Research Articles

Analysis of using femtosecond laser scanning system to impurity-induced disordering of InGaAsP quantum wells

This study is the first to demonstrate the selectivity quantum well intermixing process by using a femtosecond laser scanning-induced disordering technique. The advantages of the femtosecond laser are photochemical machining and the two-photon absorption mechanism. The femtosecond laser system can convert writing into the scan to create a nanostructure by adjusting the lens. The effect of power on the band gap shift during laser scanning was investigated. The band gap shift was small and unstable without the heating substrate. A wavelength shift higher than 77.3 nm for the InGaAsP MQW material was obtained at elevated temperatures.

Nanobeam photonic bandedge lasers

We demonstrate one-dimensional nanobeam photonic bandedge lasers with InGaAsP quantum wells at room temperature from the lowest dielectric band of photonic crystal nanobeam waveguides. The incident optical power at threshold is 0.6 mW (effectively ~18 μW). To confirm the lasing from the dielectric bandedge, the polarization and the photoluminescent spectra are taken from nanobeams of varying lattice constants. The observed shift of the lasing wavelength agrees well with the computational prediction.

Lambda shifted photonic crystal cavity laser

We propose and demonstrate an alternative type of photonic crystal laser design that shifts all the holes in the lattice by a fixed fraction of the targeted emission wavelength. The structures are realized in InGaAsP (λ=1.15) with InGaAsP quantum wells (λ=1.52) as gain material. Cavities with shifts of 1/4 and 3/4 of the emission wavelength were fabricated and characterized. Measurements show threshold behavior for several modes at room temperature. Both structures are simulated using a finite difference time domain method to identify the resonances in the spectra and calculate the mode volume of the dominant mode.

Gain-assisted propagation of surface plasmon polaritons via electrically pumped quantum wells

We studied the loss compensation of surface plasmon polaritons (SPPs) with InGaAsP quantum wells at telecom wavelength. The quantum wells are buried in the vicinity of a thin Au film. The propagation length of short-range SPPs increases drastically with the gain coefficient of quantum wells, generated by a forward bias. The elongation of SPP propagation is experimentally observed via long-range SPPs, which strongly couple with the short-range SPPs. This study paves a way for electrically manipulated amplification of SPPs in plasmonic circuits.

Effects of Ga+ milling on InGaAsP quantum well laser with mirrors milled by focused ion beam

InGaAsP/InP quantum well ridge waveguide lasers were fabricated for the evaluation of Ga+ focused ion beam milling of mirrors. Electrical and optical properties were investigated. A 7% increment in the threshold current, a 17% reduction in the external quantum efficiency, and a 15 nm blueshift in the emission spectrum were observed after milling as compared to the as-cleaved facet result. Annealing in inert atmosphere partially reverts these effects, resulting in a 4% increment in the threshold current, an 11% reduction in the external efficiency, and a 13 nm blueshift with the as-cleaved result. The current-voltage behavior after milling and annealing shows a very small increase in leakage current, indicating that optical damage is the main effect of the milling process.

Accumulated sidewall damage in dry etched photonic crystals

Evidence for accumulated damage is provided by investigating the effect of etch duration on the carrier lifetime of an InGaAsP quantum well (QW) inside the InP-based photonic crystal (PhC) structures. It is found that once the quantum well is etched through, additional etching reduces the carrier lifetimes from 800to70ps. The surface recombination velocity (SRV) at the exposed hole sidewalls is determined from the measured carrier lifetimes of the PhC fields with different lattice parameters. The observed variation in the SRV with etch duration also confirms the presence of accumulated sidewall damage. It increases from 6×103to1.2×105cms−1 as the etching time increases from 3to50min. A geometric model based on sputtering theory and on the evolution of the hole shape is developed to explain the accumulation of sidewall damage. The model is used to estimate the number of impact events from sputtered species reaching the QW sidewalls, and the variation in the accumulated impact events with etch duration is shown to be qualitatively consistent with the experimental observations. Finally, the results suggest a new method for tailoring the carrier lifetimes in PhC membrane structures.

Quantum well intermixing of a quantum well structure grown on an InAsP metamorphic pseudosubstrate on InP

InGaAsP quantum well (QW) structures, with ∼1% compressive strain, have been grown on an InAs0.21P0.79 metamorphic substrate layer (MSL) deposited on an InP substrate. For comparison, a similar QW structure is grown directly on InP. A consequence of growth on the MSL is to move the QW and barrier compositions outside the spinodal isotherm resulting in a significant reduction in phase separation. This is shown to increase the photoluminescence wavelength and improve its quality in terms of linewidth and intensity. Thermally induced QW intermixing (QWI) has also been carried out on these structures both with and without a low-temperature InP capping layer. The defects present in the underlying metamorphic buffer layers are shown to have no effect on the QWI process. However, the samples with the MSL are shown to exhibit more intermixing either due to a higher diffusion or greater P–As exchange probability in the different composition QW and barrier layers compared to the QW structure grown without the MSL, and possibly influenced by the large reduction in phase separation.

Polarization-selective resonant photonic crystal photodetector

Resonance-assisted photonic crystal (PhC) slab photodetectors are demonstrated by utilizing six 7-nm-thick InGaAsP quantum wells. In order to encourage efficient photon coupling into the slab from the vertical direction, a coupled-dipole-cavity-array PhC structure is employed. Inheriting the characteristics of the dipole mode, this resonant detector is highly polarization selective and shows a 22-nm-wide spectral width. The maximum responsivity of 0.28A∕W, which is >20 times larger than that of the identical detector without the pattern, is observed near 1.56μm.

Proton radiation effects in quantum dot lasers

Proton beams with energies of 10 and 200 MeV were irradiated onto InAs quantum dot lasers with a wavelength of 1.3 μm. The increase in threshold current by proton irradiation was small compared with those of the previously reported other quantum dot lasers with larger active region and 1.3-μm InGaAsP quantum well lasers. These results were discussed by taking account of non-ionizing energy loss and effective volume of active region.

Electrooptic Properties of InGaAsP Asymmetric Double Quantum Wells: Enhanced Slope Efficiency in Waveguide Electroabsorption Modulators

We present detailed theoretical estimates of the optical properties of InGaAsP quantum well (QW) electroabsorption modulators (EAMs) operating at ~1550 nm wavelength. Absorption coefficients of QWs are obtained from the linear optical susceptibility. Exciton states are calculated in momentum space, which includes valence-band mixing, mixing of excitons originating in different subband pairs, and exciton spin-related optical selection rules. Various line-broadening mechanisms relevant to InGaAsP-QWs are also included. Extending the study further to asymmetric double QWs (ADQWs) suggests that the small-signal modulation efficiency can be enhanced significantly at substantially lower operating bias voltage. Simple optimization of ADQW band structure results in a maximum slope efficiency ~3.8 times larger than that of SQW EAMs at a reduced operating bias field of 34 kV/cm compared with ~70 kV/cm for comparable SQWs.

All-optical bistable switching in curved microfiber-coupled photonic crystal resonators

The authors report low-power optical bistability under continuous wave pumping conditions in five-cell photonic crystal linear resonators containing InGaAsP quantum wells, by employing the fiber-coupling technique. The threshold bistable power is measured to be 35μW at the normalized detuning of −1.724. Owing to the high band-edge nonlinearities of quantum wells and the efficient fiber coupling, minimal instability is observed. In addition, all-optical switching is demonstrated with switching energy less than 75.4fJ.

Numerical study on strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting lasers

The physical and optical properties of compressively strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting lasers are numerically studied. The simulation results show that the maximum optical gain, transparency carrier densities, transparency radiative current densities, and differential gain of InGaAsP quantum wells can be efficiently improved by employing a compressive strain of approximately 1.24% in the InGaAsP quantum wells. The simulation results suggest that the 850-nm InGaAsP/InGaP vertical-cavity surface-emitting lasers have the best laser performance when the number of quantum wells is one, which is mainly attributed to the non-uniform hole distribution in multiple quantum wells due to high valence band offset.

Analysis of the linewidth enhancement factor (α-factor) in compressively strained InGaAsP quantum wire lasers

The linewidth enhancement factor (α-factor) of compressively strained (CS) InGaAsP/InP quantum wire (QWire) lasers is theoretically studied using an eight-band k⋅p formalism. It is found that tensile strained (TS) barriers lower the value of the α-factor by suppressing elastic strain relaxation. When multiple QWire layers are stacked vertically, the α-factor decreases owing to the increase in the modal gain. However, the decrease is lower than expected, because enhanced strain relaxation in multiple-layer stack tends to increase the α-factor. Comparison of the α-factors of QWires and QWells at the lasing frequency shows that the peak value of the α-factor decreases monotonically with increasing confinement, but an improvement in the α-factor of QWires at threshold condition relative to the α-factor of QWell lasers is not achieved unless the QWire width is reduced below a critical value. These results provide useful guidelines for designing CS QWire lasers with reduced values of the α-factor.

High gain, broadband InGaAs∕InGaAsP quantum well infrared photodetector

The authors design and demonstrate an InGaAs∕InGaAsP quantum well infrared photodetector for high-speed infrared detection. The InGaAsP is selected as the barrier material to provide a large photoconductive gain, and the well is made of InGaAs∕InP superlattice to achieve a broadband absorption. These features are expected to increase the photocurrent of the detector under a broadband source. For quantitative comparison, we also fabricate a quantum well GaAs∕AlGaAs superlattice detector with a similar spectrum. Dark current noise measurement indicates that the gain of the InGaAs∕InGaAsP detector is 4.6 times larger than that of the reference detector, thus confirming the present design concept.

Quantitative analysis of compositional changes in InGaAs∕InGaAsP quantum wells on GaAs induced by intermixing with a low temperature grown InGaP cap layer

Energy-dispersive x-ray spectroscopy was used to analyze quantum well intermixing between an InGaAs quantum well (QW) and InGaAsP barriers grown on GaAs induced by a low temperature, molecular beam epitaxy grown, InGaP cap. This cap layer produces an enhanced blueshift of the photoluminescence (PL) wavelength following postgrowth annealing, and degradation of the PL signal. Cross-sectional transmission electron microscopy reveals modification of the whole structure, with formation of arsenic precipitates, broadening, and subsequent disappearance of the QWs in the capped structure. Uncapped samples are relatively unchanged. Increased phosphorus observed in the QW for capped structures confirms the diffusion of phosphorus from the P-rich cap.

Photoreflectance investigations of quantum well intermixing processes in compressively strained InGaAsP∕InGaAsP quantum well laser structures emitting at 1.55μm

We have investigated the effects of interdiffusion and its technological parameters on the subband structure in compressively strained InGaAsP quantum wells (QWs) using photoreflectance and photoluminescence techniques. p-i-n laser structures with three QWs were grown by gas source molecular beam epitaxy and capped with dielectric films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition and annealed using a rapid thermal annealing process. A numerical real-time wave-packet propagation method including static electric field, strain in the wells and barriers, and error function interface diffusion modeling is used to calculate the transition energies for the diffused QWs. It has been shown that the shift of the energy levels due to the interdiffusion related changes of the well confinement potential profile is a consequence of two competing processes: a change of the well width and an effective increase of the band gap energy resulting in a net blueshift of all optical transitions. Moreover, it has been found that quantum well intermixing does not significantly influence the built-in electric fields distribution.

The effect of different proximity caps on quantum well intermixing in InGaAsP/InP QW structures

A low-temperature InP-cap layer is used to enhance quantum well intermixing (QWI) following rapid thermal annealing (RTA) on an InGaAsP quantum well (QW) structure. The influence of different proximity caps (Si, InP and GaAs) used during the RTA step has been investigated. A combination of cross-sectional transmission electron microscopy and high-resolution TEM together with energy-dispersive x-ray analysis directly reveals compositional and morphological changes resulting after QWI. Room temperature photoluminescence is used to establish the changes in emission wavelength and intensity resulting from the QW modification. Use of a Si proximity cap leads to the formation of a sharply defined QW with the least amount of QW modification, while GaAs proximity capping results in the broadest QW, broadened QW/barrier interfaces and the highest concentration of phosphorous in the well. Use of an InP proximity cap results in intermediate QW modification. In all cases, after QWI the bottoms of the QWs are flat and the well is square-like with broadened sidewalls. It has also been found that group V rich precipitates are produced on the top two layers of the structure. The concentration and size of the precipitates are minimum with Si proximity capping, while the use of GaAs produces the highest concentration and largest precipitates. The concentration and size of the precipitates are intermediate for the InP capping. The choice of proximity cap material affects the intermixing through changes of the effective P diffusivity which has been calculated from obtained profiles.

InGaAsP quantum-wells saturable absorber for diode-pumped passively Q-switched 1.3-μm lasers

We demonstrate the first use of InGaAsP quantum wells as a saturable absorber in the Q-switching of a diode-pumped Nd-doped 1.3 μm laser. The barrier layers of the InGaAsP quantum-well device are designed to be a strong absorber for the suppression of the transition channel at 1.06 μm. With an incident pump power of 1.8 W, an average output power of 160 mW with a Q-switched pulse width of 19 ns at a pulse repetition rate of 38 kHz was obtained.

Measurements of TiOx stress induced on InP∕InGaAs∕InGaAsP quantum well heterostructures

Measurements of stress induced by TiOx layers on single quantum well InP based heterostructure are presented. Strain characterization has been performed by photoluminescence (PL) and micro-Raman spectroscopy. We present a comparison of the stress induced by TiOx and SiO2 layers which are commonly used as masking material for the quantum well intermixing process. Micro-Raman spectroscopy and PL revealed that TiO2 is creating a stress field in the top layers of the heterostructure, with a dependence on temperature and stressor thickness. A hysteresis phenomenon of the Raman shift has also been observed after measurements at low temperature (below 300 K) which shows that the stress created by TiOx exceeds the elastic limit of InP. On the other hand, there is no evidence that SiO2 is inducing stress. Rapid thermal annealing of samples covered with titanium oxide results in improvement of the thermal stability.

Effect of intraband carrier relaxation on the threshold characteristics of quantum well lasers

The effect of intraband carrier relaxation on the threshold characteristics of InGaAsP quantum well (QW) lasers is studied. The dependence of the intraband hole-hole relaxation time τint on temperature and carrier density is analyzed. It is shown that taking into account the finiteness of τint and its dependence on temperature and carrier density strongly affects the gain and the threshold current density of QW lasers.