Auger recombination is known to be a significant non-radiative process limiting near- and mid-infrared quantum well lasers. The one-dimensional confinement of quantum wells and small band offsets (relative to the bandgap) permits two fundamentally different categories of Auger mechanisms to operate. These mechanisms may be identified as either activated or thresholdless in nature. In this work, we investigate the nature of the dominant Auger mechanism in mid-infrared emitting quantum wells by characterizing a range of type-I InGaAsSb quantum well lasers operating within the 2 - 3 μm wavelength range. The temperature dependence of both the threshold current density and integrated spontaneous emission reveal that the threshold current is dominated by radiative recombination up to a break-point temperature (occurring below 200 K). Beyond the break point temperature, the exponential dependence of the threshold current increases rapidly. The deterioration in the stability of lasing threshold indicates that a thermally activated Auger process is dominant in all devices and is sensitive to the population of heavy-holes in the quantum wells.

Auger recombination is known to be a significant non-radiative channel in near- and mid-infrared quantum well emitters [1] . As a result, the threshold current density of semiconductor lasers increases substantially with increasing wavelength and temperature, impacting the overall efficiency of a laser-based optoelectronic system. In an Auger process the energy released from an electron-hole recombination is transferred to a third carrier. The one-dimensional confinement of quantum wells and small band offsets (relative to the bandgap) in infrared type-I quantum well geometries permit two fundamentally different categories of Auger mechanisms to operate. We refer to these as activated or thresholdless . In a thresholdless process the absence of an activation energy means that the Auger coefficient of an Auger process varies only weakly with temperature. This contrasts with an activated process where the kinematic threshold causes the Auger coefficient to increase approximately exponentially with temperature. There is no clear consensus in the literature on the nature of Auger recombination in type-I quantum wells, and both have variously been invoked to explain the temperature and wavelength dependence of near- and mid-infrared quantum well lasers [2] , [3] .

We investigate the temperature and pressure dependence of a series of intrinsic and modulation p-doped InAs-based dot-in-well (DWELL) laser diodes grown on silicon substrates. Temperature dependence of the threshold current density (Jth) and pure spontaneous emission spectra provide an insight into inhomogeneity and non-radiative recombination mechanisms within the devices. Initial investigations showed that the intrinsic devices exhibited low temperature sensitivity in the range 170-200K. Above this, Jth increased more rapidly consistent with Auger recombination. P-doping increased the temperature at which Jth(T) started to increase up to 300K with a temperature insensitive region close to room temperature. P-doping delays the onset of carrier thermalization, leading to a high T0 but with an associated higher Jth. Temperature dependence of gain spectrum broadening was investigated by measuring the spontaneous emission spectral width parameter (1/e2) just below Jth (T). A strong direct correlation is found between the temperature dependence of peak width with the temperature dependence the radiative component of threshold, Jrad(T). At low temperature the correlation is consistent with strong inhomogeneous broadening of the carrier distribution. As temperature increases Jth reduces associated with carriers thermalizing to lower energy states. At higher temperatures homogeneous thermal broadening coupled with non-radiative recombination causes Jth to increase. Inhomogeneous broadening is more pronounced in the p-doped devices due to coulombic attraction between acceptor holes and injected electrons. A detailed analysis of recombination processes using high hydrostatic pressure and spontaneous emission in these lasers as a function of doping density will be presented and discussed at the conference.

Type-I quantum well (QW) lasers based on the GaSb material system show attractive characteristics in the mid-infrared [1]. However, as the wavelength (λ) increases in the range of 2–4 μm their performance begins to deteriorate due to increasing Auger recombination [2]. In the Auger process, the energy released from an electron-hole recombination is transferred to a third carrier. In order to develop strategies to suppress Auger recombination, it is crucial to understand the magnitude and nature of the dominant Auger recombination pathway, and their dependencies on the operating λ and temperature (T).

The temperature performance of InAs/Si quantum dot lasers is studied using temperature-dependent characterization of the stimulated and spontaneous emission and discussed in terms of localization effects due to the inhomogeneity of the active region and the interplay of radiative and non-radiative recombination.

Summary form only given. Semiconductor lasers operating in the 2-3 μm wavelength range are useful for a variety of applications including environmental monitoring, non-invasive medical diagnosis and industrial processing [1]. While type-I GalnAsSb/GaSb quantum well (QW) lasers have achieved room temperature operation up to 3.73 μm, they are limited by the effects of non-radiative Auger recombination, inter-valence band absorption and carrier leakage due to inadequate hole confinement, all of which induce sensitivity to temperature [2]. Here we report studies of the non-radiative recombination mechanisms in type-I GalnAsSb based lasers, in order to assist device optimisation [3-5].

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.

Type-I GaInAsSb lasers, emitting between 2–3 µm are investigated using temperature and high pressure characterization techniques. A model of the Auger processes is used to fit the non-radiative component of the threshold current at room temperature, identifying the dominance of different Auger losses across the wavelength range of operation.

The impact of carrier density non-pinning above threshold on laser performance is studied in different quantum dot/dash lasers with room temperature emission wavelengths of 0.98-1.52 mu m. Owing to inhomogeneity in the active region, the non-pinning may be important even above room temperature because of the non-thermal carrier distribution between the dots. This has a large impact on the external differential efficiency and the output power of the devices. In the presence of non-radiative recombination, non-pinning will further decrease the output power and the slope efficiency because of a significant reduction in the number of carriers available for stimulated emission.

This paper focuses on a new design and demonstration of a MQW laser structure which can overcome the intrinsic temperature sensitivity of the laser.

The anomalous behavior of impact ionization in dilute-nitride GaInNAs photodiodes with a range of nitrogen content below 4% is investigated. The ratio of hole- and electron-initiated ionization coefficients, k = β/α, is enhanced by a factor up to ∼4 with increasing nitrogen content. The absolute ionization coefficients are suppressed by up to two orders of magnitude at low electric fields in samples with 3% N. The narrow band gap, suppressed impact ionization, and increased breakdown voltage characteristics of GaInNAs make it a suitable material for use as part of a composite collector in GaAs-based heterojunction bipolar transistors.

In this study low temperature and high pressure techniques have been used to investigate the recombination processes taking place in InGaN-based quantum well light emitting diodes (LEDs) which have emission across the blue-green region. Despite relatively high peak efficiencies of the GaN-based emitters, there remain issues relating to the strong efficiency reduction at higher currents that are required for normal operation in most applications. It is observed that there is a relative reduction in efficiency as injection current is increased in a phenonmenon which is known as efficiency droop. There are three main arguments for the cause of efficiency droop that are discussed in the literature: non-radiative Auger recombination, carrier leakage and a defect-related loss mechanism. In spite of extensive research to date, there is little agreement on the cause of efficiency droop as most experiments can only measure the overall efficiency behaviour leading to difficulties in determining the individual contributions from the different loss mechanisms.

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.

The thermal properties of 5-stage “W” Interband-Cascade Lasers emitting at 4.1 μm at room temperature (RT) are investigated by measuring the lasing and spontaneous emission properties as a function of temperature and hydrostatic pressure up to 1 GPa. Experiments show that at RT more than 90% of threshold current of these devices is due to non-radiative loss processes. We also find that the threshold current density dependence on temperature can be fitted with a single exponential function over a wide temperature range with a characteristic temperature, T0, of 45 K. The relatively high temperature sensitivity in these devices is attributable to the large non-radiative current contribution coupled with non-pinning of the carrier density above threshold.

Two issues with using InGaAsN as absorber in avalanche photodiodes (APDs) for 1310nm wavelength applications are addressed here. Firstly, we demonstrated InGaAsN p-i-n diodes with stable photoresponse around 1310nm but reverse leakage current density slightly above the acceptable limit of ~0.2mA/cm2 at 150kV/cm. We also investigated whether or not InGaAsN as absorber is compatible with Al0.8Ga0.2As (the proposed avalanche material in our separate-absorption-multiplication APD design) in terms of the relationship between α and β in InGaAsN. Our observations suggest α ~ β in InGaAsN, making it compatible with Al0.8Ga0.2As.

The efficiency of InGaN/GaN blue-green emitters is experimentally investigated. The results provide initial evidence for an inter conduction-band Auger resonance, increasing droop in InGaN LEDs and causing the low radiative efficiency of green laser diodes.

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.

The thermal properties of 5-stage “W” Interband-Cascade Lasers emitting at 4.1μm at RT are investigated. It is shown that inter-valence band absorption coupled with non-radiative recombination govern their maximum operating temperature.

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.

In order to extend the photo response of GaAs to optical telecommunication wavelengths, In and N can be incorporated into GaAs to yield a perfect lattice match of InxGa1-xAs1-yNy with GaAs with a bandgap that strongly decreases with increasing N composition. The potential usage of such a material as photodetectors and photovoltaic applications has been reported.In this work, we investigate the dark current mechanisms in the InxGa1-xAs1-yNy material.