N. F. Massé

Carrier transport and recombination in p-doped and intrinsic 1.3μm InAs∕GaAs quantum-dot lasers

The radiative and nonradiative components of the threshold current in 1.3μm, p-doped and undoped quantum-dot semiconductor lasers were studied between 20 and 370K. The complex behavior can be explained by simply assuming that the radiative recombination and nonradiative Auger recombination rates are strongly modified by thermal redistribution of carriers between the dots. The large differences between the devices arise due to the trapped holes in the p-doped devices. These both greatly increase Auger recombination involving hole excitation at low temperatures and decrease electron thermal escape due to their Coulombic attraction. The model explains the high T0 values observed near room temperature.

Temperature dependence of the gain in p-doped and intrinsic 1.3μm InAs∕GaAs quantum dot lasers

The gain of p-doped and intrinsic InAs∕GaAs quantum dot lasers is studied at room temperature and at 350K. 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=293K, 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.

Temperature and pressure dependence of the recombination processes in 1.5μm InAs∕InP (311)B quantum dot lasers

The threshold current and its radiative component in 1.5μm InAs∕InP (311)B quantum dot lasers are measured as a function of the temperature. Despite an almost temperature insensitive radiative current, the threshold current increases steeply with temperature leading to a characteristic temperature T0≈55K around 290K. Direct observation of spontaneous emission from the wetting layer shows that some leakage from the dots to the wetting layer occurs in these devices. However, a decrease in the threshold current as a function of pressure is also measured suggesting that Auger recombination dominates the nonradiative current and temperature sensitivity of these devices.

Experimental determination of the band gap dependence of Auger recombination in InGaAs∕InP multiple quantum well lasers at room temperature

The band gap dependencies of the threshold current and its radiative component are measured using high pressure techniques. Detailed theoretical calculations show that the band gap dependence of the internal losses plays a significant role in the band gap dependence of the radiative current. Temperature dependence measurements show that the radiative current accounts for 20% of the total threshold current at room temperature. This allows us to determine the pressure dependence of the non-radiative Auger recombination current, and hence to experimentally obtain the variation of the Auger coefficient C with band gap.

The importance of recombination via excited states in InAs/GaAs 1.3μm quantum dot lasers

The optical matrix element for excited-states is significantly weaker than the ground-state leading to thermally stable radiative recombination. This is not so for non-radiative Auger recombination, causing a sharp increase in threshold current with temperature.

Recombination, transport and loss mechanisms in p-doped InAs/GaAs quantum dots

The results on the temperature dependence of the radiative and non‐radiative recombination processes in p‐doped and undoped quantum dot (QD) lasers suggest that the observed characteristics of p‐doped QDs are caused by an increase in the effective conduction band off‐set due to Columbic attraction of the extra holes and so an increased localization of electrons in the dots. This leads to an increase in the temperature at which the carriers are able to establish thermal equilibrium from T=200K in the undoped devices to ⩾320K in the p‐doped samples. Interestingly this can be used to advantage since, as the temperature increases, the improved efficiency associated with better transport between the dots can be exactly offset by the increasing rate of Auger recombination, thus leading to a temperature stable operation around room temperature.

Intrinsic Limitations of p-doped and Undoped 1.3 μm InAs/GaAs Quantum Dot Lasers

The temperature dependencies of the recombination and gain processes reveal intrinsic limitations on the performances of quantum dot lasers. Controlling the transport of the carriers using the inhomogeneous broadening makes temperature stable threshold current possible

The influence of p-doping on the temperature sensitivity of 1.3 /spl mu/m quantum dot lasers

We find that non-radiative recombination plays an important role in p-doped quantum-dot lasers. Along with carrier thermalisation effects, this is responsible for the temperature insensitive operation as observed around room temperature in these lasers.

Effect of gain saturation and nonradiative recombination on the thermal characteristics of InAs/GaAs 1.3 /spl mu/m quantum dot lasers

Gain saturation increases the radiative component, J/sub rad/, of the threshold current density, J/sub th/, and its contribution to the thermal sensitivity of J/sub th/ in short cavity or low QD density devices. However, the main cause of their thermal sensitivity is a strong non-radiative recombination.