Direct measurement of the transparency current and valence band effective masses in tensile and compressively strained InGaAs/InP multiple quantum-well laser amplifiers

Transparency current densities of 250 and 160 A/cm2 per well at the bandgap wavelength are reported for compressively and tensile strained multi quantum-well laser amplifiers. A strong wavelength dependence of the transparency current is found, due to level broadening, which shows that the threshold current of a quantum-well laser is inherently loss limited, rather than transparency limited. The spectral and polarizational dependence of the gain is measured and analyzed. From this it is concluded that the compressively (1.8%) and tensile (1.6%) strained quantum-well laser amplifiers exhibit valence band effective masses of 0.07 m0 and 0.1 m0, respectively, which shows that they both have a nearly symmetric band structure.