GAINP-(ALYGA1-Y)INP 670 NM QUANTUM-WELL LASERS FOR HIGH-TEMPERATURE OPERATION

We have examined the operation of 670 nm (AlyGa1-y)InP/GaInP quantum well lasers with different aluminium compositions (y = 0.3, 0.4, and 0.5) in the barrier/waveguide layer so as to vary the optical confinement factor and hence the threshold gain requirement, Lasers with y = 0.3 have the lowest threshold current over the range 200-400 K despite having the narrowest barrier band gap of the three structures, The measured intensity of spontaneous emission due to transitions in the well increases linearly with temperature between 280-400 K, whilst that from the barrier increases exponentially, An Arrhenius treatment of the emission from the barrier gives an activation energy of 198 meV +/- 25 meV which is in excellent agreement with the value predicted from the energy band diagram, When the experimental temperature dependence of the well and barrier contributions are removed from the measured threshold current, the remaining excess current has an activation energy of around 320 meV which is in excellent agreement with the value for thermally activated loss of electrons via the X conduction band minima. Since the X gap is insensitive to composition there is no increase in this leakage current when y is reduced so the overall effect is for the current to go dawn due to the reduced gain requirement per well.