Design and performance of InGaAsP-InP planar buried-ridge-structure lasers

It is demonstrated by the calculation of leakage-current densities and by the fabrication of planar buried-ridge-structure (PBRS) lasers emitting at 1.3 μm and 1.55 μm that neither reverse-biased junctions nor high-resistivity blocking layers are needed in the shunt-current path of InGaAsP-InP BH lasers to obtain a low threshold current, high-temperature CW operation, and high reliability, The omission of blocking layers is desirable, especially with regard to monolithic integration, because they are difficult to fabricate by large-scale production. techniques. With PBRS lasers, current confinement to the active region is achieved solely by the different turn-on voltages of the p-n heterojunction and the adjacent p-n homojunctions. In order to get an estimate of the leakage current across the p-n homojunctions, the forward bias voltage U_H across these junctions normalized by the overall forward bias voltage U and the heterojunction voltage U_Q were calculated by conformal mapping. The calculation of the leakage current I_H shows that the device performance mainly depends on the series resistance and the p-side contact stripe width. With restances below 2 Ω and contact stripe widths around 4 μm, leakage currents are negligible up to diode currents of 40 mA.