V-1 a single longitudinal and fundamental transverse mode oscillation in AlGaAs transverse junction stripe lasers

Abstract

(TSS) lasers.',* However these excellent mode properties of TJS lasers have not yet been accounted for sufficiently in the p~evious paper.2 We have investigated particularly the spectral behavior of these lasers in detail to throw light upon the mechanisms responsible for the single mode oscillation. The TJS laser studied has a GaAs Zn diffused pipn homojunction structure sandwiched between two AlGa 4s layers, in which the AlGaAs-GaAs-AlGaAs double heterostructure forms the stripe geometry, and carriers are injecled laterally through the GaAs pn junction perpendicular to [he double heterojunction planes.' The carrier concentration i.n the third layer, in which the active region formed, is chosen to be 2~10'~ ~m-~. The TJS laser has a defined three dimonsional optical waveguide in which the active region is Ihe GaAs p-region surrounded by two heterojunctions, a [1-'p boundary and a pn homojunction. The dimensions of 7'JS lasers are approximately 0.35 pm in thickness, 2.5 pm in width and 300 pm in cavity length. Typical thresh3ld currents are 40 mA at 300°K. The following results were obtained in this stu3y. Firstly, a strong saturation of the spontaneous emiss on above threshold has been first observed at room temperat Ire with cw operation in these lasers. This could be explained loy the fact that the transverse mode spreads outside the gain region owing to the weak optical confinement present in these homojunction lasers with a thin heterojunction stripe. This saturation of the spontaneous emission makes it possible to suppress the oscillation of higher order transverse rnoJes and to oscillate in the fundamental transverse mode for a wide range of the current more than three times threshokl at which catastrophic damage of the mirror occurs. Secondly, a single longitudinal mode oscillation accompanied with a strong suppression of oscillation for the ccmpeting adjacent modes occurs slightly above threshold. -i'his is attributed to a mode competition mechanism which is! an inherent property in these lasers. In well-Ilehaved lasers, the single mode oscillation accompanied with complete supp '8ssion of oscillation for the adjacent modes at threshold have been observed, which shows that the TJS laser is a halnogeneously broadened laser.