High performance buried heterostructure λ=1.5 μm InGaAs/AlGaInAs strained-layer quantum well laser diodes

Today´s fibre-optic communication system applications require semiconductor lasers with low threshold current and operating, preferably uncooled, over a wide temperature range at high speed. For the fabrication of 1.3-1.5 μm wavelength quantum well laser diodes InGaAs(P)/InGaAsP and (Al)GaInAs/Al(Ga)InAs have been studied. Despite the presence of the more difficult to handle aluminium, the latter material system is mainly of interest because of its larger conduction band offset: ΔE_c=0.72 ΔE_g against ΔE_c=0.35 ΔE_g in InGaAs/InGaAsP. In combination with quantum wells deliberately grown in a state of strain, this results in higher characteristic temperature T₀, leading to lower threshold current and higher output power, especially at elevated temperatures. Moreover, both the hole transport within the active layer and the differential gain are enhanced, leading to high speed and low chirp characteristics. However, in practical Al-containing telecommunication devices these characteristics have not been optimally exploited so far. The most common device structure for these lasers is of the ridge waveguide type, which has a higher threshold current, a more elliptical and less stable output beam, and shows more pronounced ringing under current modulation than buried heterostructure (BH) devices. In this paper, we report low-threshold and high-power Fabry-Perot (FP) and low-threshold distributed feedback(DFB) 1.5 μm strained-layer InGaAs/AlGaInAs BH lasers with semi-insulating InP current-blocking layers completely grown by low-pressure organometallic vapour phase epitaxy (LP-OMVPE). For the first time, evidence for the reliable operation of these devices is presented