Blueshift of effective band gap in n-i-p-i doping superlattices as a function of optical excitation intensity

It is a well-established fact that the luminescence peak arising from spatially indirect transitions (effective band gap E-g(eff)) of a n-i-p-i structure shifts to a higher energy when the intensity of the excitation is increased. In this article, the quantitative dependence of-the effective band gap on the excitation light intensity I-W is formulated and verified experimentally. Using AlGaAs based n-i-p-i samples, the plot of ln(I-W) versus E-g(eff) gives a slope of value 4 X 10(-21) eV(-1) which agrees well with the theoretical value of 5.2 X 10(-21) eV(-1). It is found that this blueshift is typically 50 meV for a doubling in the magnitude of the optical excitation intensity from 50 to 100 mW cm(-2). Further, it is found that the carrier lifetime decreases exponentially with an increase in the excitation intensity from zero to 500 mW cm(-2) by four orders of magnitude which also agrees well with our theoretical model. (C) 1998 American Institute of Physics. [S0021-8979(98)03302-7].