We directly measure the gain and threshold characteristics of three quantum dot laser structures that are identical except for the level of modulation doping. The maximum modal gain increases at fixed quasi-Fermi level separation as the nominal number of acceptors increases from 0 to 15 to 50 per dot. These results are consistent with a simple model where the available electrons and holes are distributed over the dot, wetting layer, and quantum well states according to Fermi-Dirac statistics. The nonradiative recombination rate at fixed quasi-Fermi level separation is also higher for the p-doped samples leading to little increase in the gain that can be achieved at a fixed current density. However, we demonstrate that in other similar samples, where the difference in the measured nonradiative recombination is less pronounced, p doping can lead to a higher modal gain at a fixed current density.

We directly measure the modal gain and spontaneous emission spectra in three quantum dot structures that are nominally identical except for the level of p doping to ascertain the effect that p doping has on quantum dot lasers. The maximum modal gain increases at fixed quasi-Fermi level separation as the level of p doping increases from 0 to 15 to 50 acceptors per dot. The internal optical mode loss is similar for all three samples but the measured nonradiative current is larger for the p-doped structures.

An Indium Arsenide Bismide photodiode has been grown, fabricated, and characterized to evaluate its performance in the Mid Wave Infrared region of the spectrum. Spectral response from the diode has been obtained up to a diode temperature of 225 K. At this temperature, the diode has a cut off wavelength of 3.95 lm, compared to 3.41 lm in a reference Indium Arsenide diode, indicating that Bismuth has been incorporated to reduce the band gap of Indium Arsenide by 75 meV. Similar band gap reduction was deduced from the cut off wavelength comparison at 77 K. From the dark current data, shunt resistance values of 8 and 39 X at temperatures of 77 and 290 K, respectively, were obtained in our photodiode. V

The authors measure the temperature dependence of the components of threshold current of 1300 nm undoped and p-doped quantum dot lasers and show that the temperature dependence of the injection level necessary to achieve the required gain is the largest factor in producing the observed negative T 0 in p-doped quantum dot lasers. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2361167͔ p-type modulation doped In͑Ga͒As quantum dot lasers have attracted much interest recently, partially due to reports of an infinite or negative characteristic temperature ͑T 0 ͒ around room temperature. 1-3 Several authors have attributed this behavior to the temperature dependence of the Auger recombination process in doped structures, 2,4,5 although the particulars of the explanation varied in each case. In this work we report on measurements made on both intrinsic and p-doped quantum dot structures that emit at 1.3 m. From studying the radiative and nonradiative components of the threshold current we show that the temperature performance of p-doped lasers can be described without needing to consider Auger recombination.Two samples were grown by solid source molecular beam epitaxy on 3 in. n + ͑100͒ GaAs substrates. The devices were nominally identical except for the level of modulation doping. The active region consisted of five dot-in-a-well ͑DWELL͒ repeats, where each DWELL was made up of 3.0 ML of InAs grown on 2 nm of In 0.15 Ga 0.85 As and then capped by a further 6 nm of In 0.15 Ga 0.85 As, and these were then separated by 50 nm GaAs spacers. The active region was incorporated into a GaAs-Al 0.4 Ga 0.6 As waveguide structure. The lower n-contact region was doped with Si at 5 ϫ 10 18 cm −3 while the upper p contact was doped with Be at 5 ϫ 10 17 cm −3 , the p contact was finished with a 300 nm layer of GaAs doped at 1 ϫ 10 19 cm −3 . The growth temperature for the cladding layers was 620°C, while the InAs layers were grown at 510°C, the GaAs spacers were grown in two temperature steps; the first 15 nm at 510°C and the final 35 nm at 580°C, forming the so called high growth temperature spacer layers. 6 The doping consisted of Be atoms incorporated over a 6 nm region of GaAs situated 9 nm below each DWELL at a concentration of either 0 or 7.5 ϫ 10 17 cm −3 corresponding to either 0 or 15 acceptor atoms per quantum dot. Previous work on these structures has shown that the absorption spectra, and therefore the quantum dot states, are the same for the two structures. 7The threshold current was measured as a function of temperature on 2000 m long, 50 m wide oxide stripe lasers for both structures under pulsed conditions with a pulse length of 400 ns and a repetition rate of 1 kHz to avoid any self-heating, and this is shown in Fig. 1. The undoped structure shows a monotonically increasing threshold current from low to high temperatures as is normally observed for undoped quantum dot and quantum well structures. The p-doped structure exhibits a threshold current density that decreases as the temperature increases from 200 K r...

The optical and electrical properties of InAs quantum dots epitaxially grown on a silicon substrate have been investigated to evaluate their potential as both photodiodes and avalanche photodiodes (APDs) operating at a wavelength of 1300 nm. A peak responsivity of 5 mA/W was observed at 1280 nm, with an absorption tail extending beyond 1300 nm, while the dark currents were two orders of magnitude lower than those reported for Ge on Si photodiodes. The diodes exhibited avalanche breakdown at 22 V reverse bias which is probably dominated by impact ionisation occurring in the GaAs and AlGaAs barrier layers. A red shift in the absorption peak of 61.2 meV was measured when the reverse bias was increased from 0 to 22 V, which we attributed to the quantum confined stark effect. This shift also leads to an increase in the responsivity at a fixed wavelength as the bias is increased, yielding a maximum increase in responsivity by a factor of 140 at the wavelength of 1365 nm, illustrating the potential for such a structure to be used as an optical modulator.