Composition analysis and distributed feedback lasers of strained InGaAsP quantum wells with constant As/P ratio

Multi-quantum well 1.55 µ m lasers using compressively strained InGaAsP wells and tensile-strained InGaAsP barriers with the same As/P ratio are advantageous with respect to thermal stability and ease of metalorganic vapor phase epitaxial (MOVPE) growth. The composition of strongly strained (≤±1.3%) quaternary layers with As content y =0.75 but different Ga contents x is analyzed using X-ray diffraction and photoluminescence, and also, for the first time, electron probe microanalysis. It is found that x and y can be determined from the mismatch and a gap energy function E g ( x , y ), as well as from a vapor-solid relation, which formerly were established to hold only for nearly lattice-matched layers. Thermal treatment of laser structures only negligibly shifted the emission wavelength. Nearly strain-compensated 2-well lasers on n- and p-substrates reveal extrapolated threshold current densities of 190 and 730 A/cm 2 , respectively, which are the lowest values reported so far for a constant- y material. Constricted-mesa 2-well DFB lasers on p-substrates show threshold currents of 10 to 20 mA and a modulation capability of 8 Gb/s.