Using modulation spectroscopy measurements of the stark effect in MOVPE grown GaAs/(AlGa)As multiple quantum wells to observe monolayer thickness changes in wells of up to 158Å in width

Abstract

We have measured complementary spectra at 17K of electro-reflectance (ER) and electro-transmission (ET), photocurrent (PC) and photoabsorption (PA), all as a function of electric field, on two GaAs/A1 0.3Ga 0.7 As multiple quantum wells (MQWs), with 60Å barriers and either 87Å or 158Å wells. Using PC or PA, we detect very weak splittings of the principal excitonic features. Using the modulation techniques (ER or ET), the splittings exhibit a much stronger signature, which can be followed up to large values of electric field applied perpendicular to the wells. We deduce that the splittings are caused by monolayer changes in well width at clearly defined depths in the MQW stack. The imperfections of the stack have important consequences for MOVPE-grown optoelectronic devices based on MQWs.