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 μm, compared to 3.41 μm 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 Ω at temperatures of 77 and 290 K, respectively, were obtained in our photodiode.

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.

The authors measure the temperature dependence of the components of threshold current of 1300nm 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 T0 in p-doped quantum dot lasers.

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.

The role of changes in gain and nonradiative recombination as a function of temperature in p-doped quantum dot samples that exhibit a minimum in the threshold current versus temperature characteristics are examined using a detailed analysis based on the multisection measurement method. An injection level is defined as the difference between the transparency energy and the transition energy of the dot states so that the results at different temperatures may be compared. The temperature dependence of the injection level necessary to achieve the required gain produces the initial decrease in nonradiative recombination current and threshold current between 250-280 K. At higher temperatures, the nonradiative recombination increases due to both an increase in the injection level required to achieve a fixed value of gain and because of an increase in the nonradiative recombination at fixed injection level. Using measurements of the population inversion function it is shown that the reduction in the injection level required to achieve a fixed value of gain between 250-280 K is caused by the thermalization of the carrier distribution over this temperature range. Subsequent increases in the injection level required to achieve a fixed value of gain are due to the increasing thermal distribution of carriers over the available states at higher temperatures.

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.