Direct gap related optical transitions in Ge/SiGe quantum wells

An experimental study of the direct-gap related optical transitions in strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells (MQWs) is presented. These structures are of particular interest due to the proximity of Γ-type and L-type conduction band states and due to their type I band alignment. The samples were grown by low-energy plasma-enhanced CVD and consist of Ge MQWs with a large numbers of periods and good morphological quality grown onto thick graded Si1-xGex buffer layers. The transmission spectra, which shows clear evidence of excitonic transitions, are studied as a function of temperature in the 5–300 K range. Preliminary results of photocurrent measurements performed on the same structures using metal–semiconductor–metal contact are discussed.