The gain of p-doped and intrinsic InAs/ GaAs quantum dot lasers is studied at room temperature and at 350 K. Our results show that, although one would theoretically expect a higher gain for a fixed carrier density in p-doped devices, due to the wider nonthermal distribution of carriers amongst the dots at T = 293 K, the peak net gain of the p-doped lasers is actually less at low injection than that of the undoped devices. However, at higher current densities, p doping reduces the effect of gain saturation and therefore allows ground-state lasing in shorter cavities and at higher temperatures. Due to the large volume of data being readily transferred between network users, there is an increasing demand for "fiber-to-the-home" based optical fiber networks which require fast and temperature insensitive semiconductor lasers emitting at 1.3 m. Despite significant progress in reducing the threshold current densities ͑J th ͒ or improving the temperature stability, 1,2 intrinsic quantum dot ͑QD͒ lasers emitting around 1.3 m have yet to meet their full potential. This is attributed to many factors such as inhomogeneous broadening or size dispersion of the dots and dominating nonradiative recombination at room temperature ͑RT͒ which increases J th and its sensitivity to temperature variations. 3,4 It has been proposed that p-doping the devices and thus saturating the levels in the valence band with holes would greatly improve the device performance by increasing the gain and the bandwidth. 5,6 Although the effect of p-doping shows major improvements on the temperature sensitivity and the bandwidth of the devices, 7 measurements do not show a clear enhancement of the gain for a given injection 8 as it is expected from theory. 5,6 Recent results reported that the superior thermal stability of InAs/ GaAs p-doped QD lasers around room temperature arises from a combination of improving thermal distribution of the electrons, leading to a decrease in the radiative current necessary to reach the lasing threshold, and an increase in nonradiative Auger recombination with temperature, together giving rise to a constant threshold current over a limited temperature range. 4 In this work, we consider the temperature sensitivity of the gain and specifically, the effect of the nonthermal distribution of the carriers on the gain characteristics of p-doped devices and compare the results to those obtained with intrinsic quantum dot lasers.The gain was measured using the method described by Hakki and Paoli 9 at both room temperature, where carriers in the intrinsic devices are in thermal equilibrium, and at 350 K, where carriers in the p-doped lasers are expected to be closer to thermal equilibrium. 4 The lasing wavelength of the devices was approximately 1.28 m at room temperature. The active region consisted of ten stacked InAs dot-ina-well layers separated by either modulation p-doped or intrinsic GaAs barriers sandwiched by GaAs waveguide and AlGaAs cladding layers. The chips were driven with 50 s long pulses at a duty cycle of 50%. The...
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.
We report calculations of the strain dependence of the piezoelectric field within InGaN multi-quantum wells light emitting diodes. Such fields are well known to be a strong limiting factor of the device performance. By taking into account the nonlinear piezoelectric coefficients, which in particular cases predict opposite trends compared to the commonly used linear coefficients, a significant improvement of the spontaneous emission rate can be achieved as a result of a reduction of the internal field. We propose that such reduction of the field can be obtained by including a metamorphic InGaN layer below the multiple quantum well active region. © 2013 AIP Publishing LLC
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