InGaAsP Quantum Research Articles

InGaAsP VECSEL for watt-level output at a wavelength around 765 nm.

We demonstrate a deep-red-emitting vertical external-cavity surface-emitting laser (VECSEL) with an emission wavelength around λ = 765 nm based on InGaAsP/GaInP quantum wells. The quaternary material system was characterized with x-ray diffraction of thin films as the basis for InGaAsP quantum wells, which are incorporated into an 11 × 1 quantum well active region. The surface morphology of the fabricated VECSEL structure is analyzed with atomic force microscopy and the laser is evaluated in a linear cavity for various heatsink temperatures resulting in a watt-level output power of Pmax,-15°C = 1.71 W in a fundamental transverse mode.

Evanescently Coupled DBR Laser Arrays in the 760–770 nm Wavelength Range

In this letter, we present evanescently coupled semiconductor laser arrays designed with a distributed Bragg reflector section for spectrally narrow emission and a combined waveguide section for high optical output powers. These devices were designed and fabricated in the AlGaAs material system with an InGaAsP quantum well providing emission in the 760–770 nm wavelength range. Measurements of the light-current characteristics reveal high optical output powers of 600 mW at 20 °C and 700 mW at 5 °C limited by thermal rollover without any signs of a catastrophic optical mirror damage or rapid power degradation. Spectrally narrow emission of 0.2 nm at −3 dB and a high wavelength stability with a small current tuning coefficient of 0.7 pm/mA were found. Far-field investigations reveal pre-dominant coupling of lowest order in-phase supermode emission without any sections for adjusting the phase of the electrical field vector for adjacent elements.

Epitaxial Growth of Optically Thick, Single Crystalline Silver Films for Plasmonics.

Single crystalline Ag films on dielectric substrates have received tremendous attention recently due to their technological potentials as low loss plasmonic materials. Two different growth approaches have been used to produce single crystalline Ag films previously. One approach is based on repetitive cycles of a two-step process (low temperature deposition followed by RT annealing) using molecular beam epitaxy (MBE), which is extremely time-consuming due to the need for repeat growth cycles. Another approach is based on rapid e-beam deposition which is capable of growing thick single crystalline Ag films (>300 nm) but lacks the precision in thickness control of thin epitaxial films. Here, we report a universal approach to grow atomically smooth epitaxial Ag films by eliminating the repetitive cycles used in the previous two-step MBE method while maintaining the precise thickness control from a few monolayers to the optically thick regime, thus overcoming the limitations of the two aforementioned methods. In addition, we develop an in situ growth of aluminum oxide as the capping layer to protect the epitaxial Ag films. The quality of the epitaxial Ag films was evaluated using a variety of techniques, and the superior optical performance of the films is demonstrated by measuring the propagation length of surface plasmon polaritons (∼80 μm at 632 nm) as well as their capability to support a plasmonic nanolaser in infrared incorporating an InGaAsP quantum well as the gain media.

On-Chip Photonic Crystal Surface-Emitting Membrane Lasers

Photonic crystal lasers can be realized either based on photonic bandgap defect mode or defect-free bandedge mode, while the bandgap is not essential for the latter. We review here defect-free bandedge mode based photonic crystal surface-emitting lasers (PCSELs) for on-chip integration. We first discuss ultra-thin membrane reflector vertical-cavity surface-emitting lasers (MR-VCSELs), where single layer photonic crystal slabs can be designed as a broadband membrane reflector. Later, we discuss another type of defect-free PCSELs where the lasing cavity is formed based on evanescent coupling of gain medium with the photonic crystal bandedge mode near bandedge. Cavity designs were carried out for the optimal modal overlap and high confinement factors. Lateral cavity size scaling was also investigated both theoretically and experimentally in PCSELs. Buried tunnel junction based InGaAsP quantum well heterostructures were also designed and incorporated into electrically injected PCSELs. Finally, discussions are given toward energy efficient lasers.

Quantitative experimental assessment of hot carrier-enhanced solar cells at room temperature

In common photovoltaic devices, the part of the incident energy above the absorption threshold quickly ends up as heat, which limits their maximum achievable efficiency to far below the thermodynamic limit for solar energy conversion. Conversely, the conversion of the excess kinetic energy of the photogenerated carriers into additional free energy would be sufficient to approach the thermodynamic limit. This is the principle of hot carrier devices. Unfortunately, such device operation in conditions relevant for utilization has never been evidenced. Here, we show that the quantitative thermodynamic study of the hot carrier population, with luminance measurements, allows us to discuss the hot carrier contribution to the solar cell performance. We demonstrate that the voltage and current can be enhanced in a semiconductor heterostructure due to the presence of the hot carrier population in a single InGaAsP quantum well at room temperature. These experimental results substantiate the potential of increasing photovoltaic performances in the hot carrier regime. Hot carrier solar cells promise efficiencies above the thermodynamic limit but the hot carrier effects remain elusive so far. Here, Nguyen and Lombez et al. quantify the hot carrier contribution to the voltage and current of a micrometre-scale solar cell operating at room temperature, with an efficiency up to ~11%.

Effect of occupation of the excited states and phonon broadening on the determination of the hot carrier temperature from continuous wave photoluminescence in InGaAsP quantum well absorbers

AbstractAn InGaAsP quantum well with a type‐II band alignment is studied using continuous wave power and temperature dependent photoluminescence (PL) spectroscopy. The small energy separation between the ground state and first excited state results in significant thermal carrier redistribution and excited state occupation, particularly, with increasing excitation power and temperature. This state filling is evident as a high‐energy shoulder in the PL spectra, the same energy region where in the simplest Planck‐description the gradient is considered inversely proportional to carrier temperature. The outcome of an excited state occupation in broadening the high‐energy PL tail is to perturb the temperature extracted using this analysis; therefore, the true temperature of carriers is not properly evaluated when significant state filling occurs. In addition, broadening of the PL due to phonons at higher temperatures also distorts (or falsely increases) the non‐equilibrium “hot” carrier temperature and as such should be considered when using Planck's relation. The role of these two effects is considered and their mutual effect on the analysis of the extracted hot carrier temperature discussed. Copyright © 2017 John Wiley & Sons, Ltd.

The effects of external strain on the gain of InGaAsP quantum well

The effects of external strain on the gain of InGaAsP quantum well

Printed Large-Area Single-Mode Photonic Crystal Bandedge Surface-Emitting Lasers on Silicon.

We report here an optically pumped hybrid III-V/Si photoic crystal surface emitting laser (PCSEL), consisting of a heterogeneously integrated III-V InGaAsP quantum well heterostructure gain medium, printed on a patterned defect-free Si photonic crystal (PC) bandedge cavity. Single mode lasing was achieved for a large area laser, with a side-mode suppression ratio of 28 dB, for lasing operation temperature ~200 K. Two types of lasers were demonstrated operating at different temperatures. Detailed modal analysis reveals the lasing mode matches with the estimated lasing gain threshold conditions. Our demonstration promises a hybrid laser sources on Si towards three-dimensional (3D) integrated Si photonics for on-chip wavelength-division multiplex (3D WDM) systems for a wide range of volume photonic/electronic applications in computing, communication, sensing, imaging, etc.

Research on MeV pulsed radiation detection based on refractive index modulaiton

High time resolution detecting systems for MeV pulsed radiation are essential for inertial confinement fusion diagnostics. Traditional detection of system time resolution is restricted by cable bandwidth. Based on recording excess carrier dynamics in semiconductors, a new detecting mechanism, called RadOptic, was developed by Lawrence Livermore National Laboratory (LLNL). The variation of intensity of pulsed radiation with time was converted into the variation of intensity of infrared laser probe by using this mechanism. The sensing material was InGaAsP quantum wells with severalmicrometer thickness. Picosecond time resolution for several keV pulsed radiation has been demonstrated. The reported system is not suitable for MeV pulses due to its low efficiency to MeV photons. Multiple cascaded structure for MeV photon to electron transformation was proposed by LLNL. Applying bulk material with several-hundredmicrometer thickness is an alternative. Based on transient free carrier absorption, a system recording bulk materials' instantaneous refractive index change is established. The system consists of a probe laser, an interferometer module, a signal transmission module and a signal recording module. The probe is a tunable infrared continuous wave laser whose wavelength is ~1453 nm, guided by single mode fiber to the interferometer. The interferometer consists of a single mode fiber head coupled directly with the polished face of a bulk semiconductor. The interference pattern forms by multiple beams reflected from the front face and the back face of the bulk. Part of interference light is coupled to the single mode fiber and forms the output signal. Pulsed radiation will deposit energy and generate excess carriers in the bulk material. The refractive index of the bulk material changes therewith according to the Drude model. The interference pattern and the light coupled to the single mode fiber also change therewith. The signal is transmitted by a long single mode fiber. The signal recording module consists of photoelectric detectors and a digital oscilloscope. The signal generation process and the time resolution of the system are analyzed. Intrinsic GaAs refractive index change is exploited under electron pulses and X ray pulses. The analysis of signal generation process shows that when the excess carriers recombine much faster/much slower than the pulse width, the output signal/output signal differential can be viewed as a measure of intensity variation with time of the incident pulse. For this prototype system, the time resolution is restricted by the digital oscilloscope to 1 GHz. Bulk intrinsic GaAs demonstrates 30 ns refractive index response time, which is longer than the incident pulse width. The differential signal can be viewed as a measure of incident pulse intensity when GaAs is exposed to 1 ns~0.2 MeV electrons pulses. The differential signal width is shorter than the pulse width when GaAs is exposed to 5 ns~0.2 MeV electrons pulses. Auger recombination process may occur in the pulse duration under this situation. The differential signal width is longer than the pulse width when GaAs is exposed to 1 ns~0.2 MeV X ray pulses. The poor signal to noise ratio affects the signal. The excess carrier generation process may be longer than theoretically estimated one under X ray pulse incident situation. The generation process and recombination process of excess carriers in GaAs show very different characteristics compared with optical excitation. The relationship between the system output signal and the incident pulsed radiation depends on the type of the incident radiation. With carefully considering the effects from incident pulse type and transient carriers density, the system can be used to detect ~MeV pulsed radiation. With an upgraded recording module, the system would demonstrate much higher time resolution.

Compact Tunable Laser With InGaAsP Photonic Crystal Nanorods for C-Band Communication

In this study, an ultracompact tunable laser with InGaAsP photonic crystal nanorods for optical communication was demonstrated within 10-μm footprint. The square photonic crystal nanorods with the InGaAsP quantum wells were fabricated and embedded in a flexible polydimethylsiloxane substrate. The high-quality single mode lasing with low threshold around the symmetry point Γ was achieved in experiments. The lasing wavelength can be linearly fine-tuned by varying the extension percentage of photonic crystals and the wavelength tunable range covers the whole conventional band communication ambit. The lasing wavelength shift is attributed to the PhC lattice distortion, and its tuning behavior agrees with the 3-D simulation results. This ultrasmall, wide-range wavelength tunable laser can function as a novel light source for the chip-scale photonic integrated circuits and optics communication system.

Gain-enhanced high-k transmission through metal-semiconductor hyperbolic metamaterials

We analyze the steady-state transmission of high-momentum (high-$k$) electromagnetic waves through metal-semiconductor multilayer systems with loss and gain in the near-infrared (NIR). Using a semi-classical optical gain model in conjunction with the scattering matrix method (SMM), we study indium gallium arsenide phosphide (InGaAsP) quantum wells as the active semiconductor, in combination with the metals, aluminum-doped zinc oxide (AZO) and silver (Ag). Under moderate external pumping levels, we find that NIR transmission through Ag/InGaAsP systems may be enhanced by several orders of magnitude relative to the unpumped case, over a large angular and frequency bandwidth. Conversely, transmission enhancement through AZO/InGaAsP systems is orders of magnitude smaller, and has a strong frequency dependence. We discuss the relative importance of Purcell enhancement on our results and validate analytical calculations based on the SMM with numerical finite-difference time domain simulations.

Carrier quenching in InGaP/GaAs double heterostructures

Photoluminescence measurements on a series of GaAs double heterostructures demonstrate a rapid quenching of carriers in the GaAs layer at irradiance levels below 0.1 W/cm2 in samples with a GaAs-on-InGaP interface. These results indicate the existence of non-radiative defect centers at or near the GaAs-on-InGaP interface, consistent with previous reports showing the intermixing of In and P when free As impinges on the InGaP surface during growth. At low irradiance, these defect centers can lead to sub-ns carrier lifetimes. The defect centers involved in the rapid carrier quenching can be saturated at higher irradiance levels and allow carrier lifetimes to reach hundreds of nanoseconds. To our knowledge, this is the first report of a nearly three orders of magnitude decrease in carrier lifetime at low irradiance in a simple double heterostructure. Carrier quenching occurs at irradiance levels near the integrated Air Mass Zero (AM0) and Air Mass 1.5 (AM1.5) solar irradiance. Additionally, a lower energy photoluminescence band is observed both at room and cryogenic temperatures. The temperature and time dependence of the lower energy luminescence is consistent with the presence of an unintentional InGaAs or InGaAsP quantum well that forms due to compositional mixing at the GaAs-on-InGaP interface. Our results are of general interest to the photovoltaic community as InGaP is commonly used as a window layer in GaAs based solar cells.

Controllable red and blue shifting of InGaAsP quantum well bandgap energy for photonic device integration

We demonstrate bandgap tuning of InGaAsP multiple quantum well structures by utilizing an impurity-free vacancy diffusion technique. Substantial modification of the bandgap energy toward the red and blue parts of the spectrum has been observed using SiO2/SiOyNx/SiNx capping layers and by controlling the associated oxygen and nitrogen content. The resulting degree of tuning, up to 120 nm red shift and 140 nm blue shift of the band-to-band wavelength emission, has been studied using room-temperature photoluminescence, in agreement with the emission spectra obtained from semiconductor optical amplifier waveguide strips.

Lasing characteristics of InP-based InAs quantum dots depending on InGaAsP waveguide conditions.

We report the influences of a dot-in-a-well structure with a thin GaAs layer and the thickness of a waveguide (WG) on the lasing characteristics of InAs quantum dots (QDs) based on InP. The QD laser diodes (QDLDs) consist of seven-stacked InAs QDs separated by a 10 nm-thick InGaAsP (1.15 μm, 1.15Q-InGaAsP) layer, which is further sandwiched by a 800 nm-thick 1.15Q-lnGaAsP WG (reference QDLD). For comparison, the InAs QDs were inserted into the InGaAsP (1.35 μm, 1.35Q-InGaAsP) quantum well embedded in the 1.15Q-InGaAsP matrix at the active layer. And a 2 monolayer (ML)-thick GaAs layer was additionally introduced right before the QD layer (GDWELL-LDs). Lasing emission from the reference QDLD with only the 1.15Q-InGaAsP structure was not observed at room temperature (RT). However, the lasing emission from the GDWELL-LDs was clearly observed at the wavelength of 1.46 μm at RT under continuous-wave (CW) mode. The threshold current density of the GDWELL-LD with the 800 nm-thick InGaAsP WG was measured to be 830 A/cm2, which was lower than that of the GDWELL-LD with the 200 nm-thick WG (900 A/cm2). Also, the slope efficiency of the GDWELL-LD was significantly improved with increasing thickness of the InGaAsP WG.

Fano Resonance Photonic Crystal Membrane Lasers and Filters for Integrated Silicon Photonics

Fano resonance, known from atomic physics, has been employed for a wide variety of nanophotonic structures, such as quantum dots, photonic crystal, plasmonics, and metamaterials, and so on. With modal dispersion engineering, Fano filters and reflectors can all be realized in single layer dielectric photonic crystal structures. Based on Fano resonance principle in 2D air hole photonic crystal slabs, combined with crystalline semiconductor nanomembrane transfer printing techniques, we have demonstrated a range of ultra-compact high performacne photonic and electronic devices on silicon and on flexible substrates.By sandwiching InGaAsP quantum well cavity in between two single –layer silicon Fano resonance photonic crystal membrane reflectors (MR), membrane reflector vertical-cavity surface- emitting lasers (MR-VCSELs) were proposed and demonstrated. We will report our recent progresses on this new type of membrane lasers, which can be built on silicon, and on flexible substrates.Ultra-compact high quality factor optical filters have also been realized experimentally, based on Fano resonances in single or coupled bi-layer photonic crystal slabs, without or with lattice displacements. Theoretically, with the control of lattice displacement between two coupled photonic crystal slabs layers, optical filter Q factors can approach 211,000,000 or infinite. Experimentally optical filters with quality factors up to 80,000 have been demonstrated. Finally, we will review other type of Fano resonance based optical structures, such as vertical to in-plane couplers, and beam routing structures, for integrated silicon photonics. The convergence of nanomembranes and Fano resonance photonic crystals offer unprecedented opportunities for unique electronic and photonic devices for 3D multi-functional Si CMOS photonics, flexible, bio-inspired/integrated photonic/electronic systems, and multi-spectral multi-color infrared imaging and sensing systems, etc. The work was supported by US AFOSR, ARO and NSF.

155-μm VCSEL with polarization-independent HCG mirror on SOI

We designed and fabricated a vertical-cavity surface-emitting laser (VCSEL) incorporating a polarization-independent high-index-contrast subwavelength grating (HCG) mirror on silicon-on-insulator (SOI) for a novel polarization-bistable device on a silicon substrate. The VCSEL consists of the HCG mirror, an active layer with InGaAsP quantum wells having optical gain around 1.55 μm, and an Al0.9Ga0.1As/Al0.16Ga0.84As DBR. We used direct wafer bonding for the bonding between the active layer and the AlGaAs DBR, and benzocyclobutene (BCB) bonding for the bonding between the active layer and the polarization-independent HCG mirror. The reflectivity of the HCG embedded with BCB was measured, resulting in a 200-nm-high reflectivity band with reflectivity higher than 99% and a small polarization dependence of ± 1%. We achieved lasing of the fabricated HCG-VCSEL at 1527 nm under an optical short pulse excitation with an average power of 50 mW (~0.2 mJ/cm2) at 240 K.

Enhanced and suppressed spontaneous emission from a buried heterostructure photonic crystal cavity

We study spontaneous emission control in a buried-heterostructure (BH) photonic crystal (PhC) cavity in which InGaAsP quantum wells (QWs) are embedded in an InP PhC. Spontaneous emission from QW-PhC cavities have been extensively investigated, but they suffer from poor carrier confinement and surface non-radiative recombination. Therefore, the clear spontaneous emission control has been only observed in quantum dots PhC cavities. The present study shows that the BH-QW-PhC cavities can exhibit distinctive spontaneous emission control in QW-PhCs. We observed large emission-rate ratio between the on- and off-resonant conditions of 30:1. This is the highest ratio reported for QW-PhCs.

Dual-rail nanobeam microfiber-coupled resonator

A microfiber-coupled dual-rail nanobeam resonator is proposed and demonstrated. The dual-rail scheme is employed to encourage the overlap between the light emitter and the air mode. The one-dimensional resonant cavity is formed by contacting a curved microfiber with the dual-rail nanobeam. The finite width of the dual-rail nanobeam turns out to be advantageous for both out-coupling with the microfiber and broader tuning of resonant wavelength. By employing InGaAsP quantum well gain medium, a simple and robust reconfigurable laser is created. Experimentally we measure a quality factor of 11,000 and out-coupling efficiency of 30%. The spontaneous emission factor (β) of the nanobeam laser is measured to be 0.16. Computationally we identified a resonant cavity with a quality factor over 6 × 10(5) and out-coupling efficiency over 90%.

Transfer-printed stacked nanomembrane lasers on silicon

A hybrid laser that combines silicon photonic-crystal reflectors with transfer-printed InGaAsP quantum wells offers a convenient means of realizing surface-emitting lasers on silicon.

Analysis of linewidth enhancement factor for compressively strained AlGaInAs and InGaAsP quantum well lasers

We have compared and analyzed theoretical investigation for the possibility of extreme reductions in the linewidth enhancement factor (α-factor) in strained layer quantum-well (QW) lasers between AlGaInAs and InGaAsP material. Valence band effective masses and optical gain in both types of QW lasers under compressive strain have been calculated using 4 × 4 Luttinger–Kohn Hamiltonian. We have used Kramers–Kronig relations to calculate the refractive index change due to carrier induced. The α-factor was up to 1.61 times smaller in AlGaInAs QW than in InGaAsP QW laser. The material differential modal gain and carrier induced refractive index change was found to be approximately 1.38 times larger and 1.15 times smaller respectively, in the previous material QW than in the latter QW laser. We also compared our results to the previously reported results for both QWs lasers.