Direct measurement of lateral carrier leakage in 1.3-μm InGaAsP multiple-quantum-well capped mesa buried heterostructure lasers

1.3-μm InGaAsP multiple-quantum-well (MQW) capped mesa buried heterostructure (CMBH) lasers with mesa widths ranging from 1 μm (standard single mode) to 100 μm (wide area) were fabricated on one wafer with identical current blocking layers at the sides. The single-mode devices had three times larger nominal threshold current density than the wide-area devices. Measurement of gain and loss in the devices showed the single-mode devices to have 6-8 cm^-1 higher loss and 40% lower optical confinement than the wide-area devices. Beyond these differences, the measurements show that up to 30% of the threshold current in the single-mode CMBH lasers does not contribute to the pumping of the MQW active region. Injection efficiency is measured to be close to unity for both single-mode and wide mesa devices. Scenarios to explain this parasitic current are discussed, including the potential role for nonradiative recombination centers at the regrown epitaxial interface, which can be consistent with all of the experimental results.