Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs)

GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mid-infrared spectral range between 2 and 3 micrometres are of great importance for low cost gas monitoring applications. This paper discusses the efficiency and temperature sensitivity of the VCSELs emitting at 2.6 μm and the processes that must be controlled to provide temperature stable operation. We show that non-radiative Auger recombination dominates the threshold current and limits the device performance at room temperature. Critically, we demonstrate that the combined influence of non-radiative recombination and gain peak – cavity mode de-tuning determines the overall temperature sensitivity of the VCSELs. The results show that improved temperature stable operation around room temperature can only be achieved with a larger gain peak – cavity mode de-tuning, offsetting the significant effect of increasing non-radiative recombination with increasing temperature, a physical effect which must be accounted for in mid-infrared VCSEL design

Challenges for room temperature operation of electrically pumped GeSn lasers

Recent demonstrations of room-temperature lasing in optically pumped GeSn show promise for future CMOS compatible lasers for Si-photonics applications. However, challenges remain for electrically pumped devices. Investigation of the processes that limit device performance is therefore vital in aiding the production of future commercial devices. In this work, a combined experimental and modelling approach is utilised to explore the dominant loss processes in current devices. By manipulating the band structure of functioning devices using high hydrostatic pressure techniques at low temperature, the dominant carrier recombination pathways are identifed. This reveals that 93±5% of the threshold current is attributable to defect-related recombination at a temperature, T = 85 K. Furthermore, carrier occupation of L-valley states (carrier leakage) is responsible for 1.1± 0.3% of the threshold current, but this sharply increases to 50% with a decrease of just 30 meV in the L-r separation energy. This indicates that thermal broadening of a similar order may reproduce these adverse efects, limiting device performance at higher temperatures. Temperature dependent calculations show that carrier occupation of indirect valley L-states strongly afects the transparency carrier density and is therefore very sensitive to the Sn composition, leading to an efective operational temperature range for given Sn compositions and strain values. Recommendations for future device designs are proposed based on band structure and growth optimisations

A comparative study of epitaxial InGaAsBi/InP structures using Rutherford backscattering spectrometry, X-ray diffraction and photoluminescence techniques

In this work, we used a combination of photoluminescence (PL), high resolution X-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) techniques to investigate material quality and structural properties of MBE-grown InGaAsBi samples (with and without an InGaAs cap layer) with targeted bismuth composition in the 3%–4% range. XRD data showed that the InGaAsBi layers are more homogeneous in the uncapped samples. For the capped samples, the growth of the InGaAs capped layer at higher temperature affects the quality of the InGaAsBi layer and bismuth distribution in the growth direction. Low-temperature PL exhibited multiple emission peaks; the peak energies, widths, and relative intensities were used for comparative analysis of the data in line with the XRD and RBS results. RBS data at a random orientation together with channeled measurements allowed both an estimation of the bismuth composition and analysis of the structural properties. The RBS channeling showed evidence of higher strain due to possible antisite defects in the capped samples grown at a higher temperature. It is also suggested that the growth of the capped layer at high temperature causes deterioration of the bismuth-layer quality. The RBS analysis demonstrated evidence of a reduction of homogeneity of uncapped InGaAsBi layers with increasing bismuth concentration. The uncapped higher bismuth concentration sample showed less defined channeling dips suggesting poorer crystal quality and clustering of bismuth on the sample surface

Improved Optoelectronic Properties of Rapid Thermally Annealed Dilute Nitride GaInNAs Photodetectors

We investigate the optical and electrical characteristics of GaInNAs/GaAs long-wavelength photodiodes grown under varying conditions by molecular beam epitaxy and subjected to postgrowth rapid thermal annealing (RTA) at a series of temperatures. It is found that the device performance of the nonoptimally grown GaInNAs p-i-n structures, with nominal compositions of 10% In and 3.8% N, can be improved significantly by the RTA treatment to match that of optimally grown structures. The optimally annealed devices exhibit overall improvement in optical and electrical characteristics, including increased photoluminescence brightness, reduced density of deep-level traps, reduced series resistance resulting from the GaAs/GaInNAs heterointerface, lower dark current, and significantly lower background doping density, all of which can be attributed to the reduced structural disorder in the GaInNAs alloy.© 2012 TMS

Temperature insensitive quantum dot lasers: Are we really there yet?

Twenty five years ago Arakawa suggested that by confining carriers in three dimensions (in quantum dots) a temperature insensitive threshold current (Ith) could be achieved in semiconductor lasers. In this paper we discuss investigations on state-of-the-art 1.3 μm InAs/GaAs undoped and p-doped quantum dot lasers for telecommunication applications and discuss the extent to which this original hypothesis has been verified. In this study, the threshold current and its radiative component (Irad) are measured as a function of temperature and pressure. The results show that although the radiative component of the threshold current can be temperature insensitive in undoped quantum dot lasers, a strong contribution from non-radiative Auger recombination makes the threshold current highly temperature sensitive. We find that p-doped devices can have a temperature insensitive Ith over a limited range around room temperature resulting from an interplay between an increasing non-radiative Auger current and decreasing radiative current. The decrease in Irad, also observed below 200 K in undoped devices, is attributed to an improvement in the carrier transport with increasing temperature. Gain measurements show that even if p-doping is successful in reducing the effect of gain saturation, the modal net gain of p-doped devices is less than in undoped lasers due to increased non-radiative recombination and non-thermal carrier distribution

Bismuth-based semiconductors for mid-infrared photonic devices

Owing to the versatile band-structure made possible through the introduction of bismuth in III-V systems, we discuss the potential to produce efficient emitters and detectors in the mid-infrared based upon conventional GaAs and InP substrates

Physical Properties of Short Wavelength 2.6μm InAs/AlSb-based Quantum Cascade Lasers

We used high hydrostatic pressure techniques to understand the deteriorating temperature performance with decreasing wavelength of short wavelength quantum cascade lasers. Influence of inter-valley scattering and distribution of the electron wave functions will be discussed

Gain peak-cavity mode alignment optimisation in buried tunnel junction mid-infrared GaSb vertical cavity surface emitting lasers using hydrostatic pressure

High-pressure techniques are used to investigate and optimise the design of GaInAsSb/AlGaAsSb vertical cavity surface emitting lasers (VCSELs) emitting at 2.4 µm. From measurements on edge emitting lasers it is found that non-radiative Auger recombination accounts for up to 85% of the threshold current at room temperature (RT) and is responsible for their strong temperature sensitivity. The effect of Auger recombination in VCSELs may be mitigated through judicious design of the gain peak–cavity mode (CM) alignment which may be investigated using high pressure. Results show that temperature insensitivity over the range −10 to +30°C may be obtained around RT if the gain peak is offset by approximately 10 meV higher in energy from the VCSEL CM

Recombination mechanisms and band alignment of GaAs1-xBi x/GaAs light emitting diodes

We investigate the temperature and pressure dependence of the light-current characteristics and electroluminescence spectra of GaAs1−xBix/GaAs light emitting diodes. The temperature dependence of the emission wavelength shows a relatively low temperature coefficient of emission peak shift of 0.19 ± 0.01 nm/K. A strong decrease in emission efficiency with increasing temperature implies that non-radiative recombination plays an important role on the performance of these devices. The pressure coefficient of the GaAs0.986Bi0.014 bandgap is measured to be 11.8 ± 0.3 meV/kbar. The electroluminescence intensity from GaAsBi is found to decrease with increasing pressure accompanied by an increase in luminescence from the GaAs cladding layers suggesting the presence of carrier leakage in the devices