A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques.After bonding,a single KrF (248 nm) excimer laser pulse was directed through the transparent sapphire substrates followed by low-temperature heat treatment to remove the substrates.The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN films were investigated systemically.Atomic force microscopy,X-ray diffraction and photolumi-nescence measurements showed that (1) the quality of the GaN film was higher at a lower bonding temperature and lower energy density;(2) the threshold of the energy density of the excimer laser lift-off GaN was 300 mJ/cm 2.The root-mean-square roughness of the transferred GaN surface was about 50 nm at a bonding temperature of 400°C.
The hole subband structures and effective masses of tensile strained Si/Si1yGey quantum wells are calculated by using the 6×6 k·p method.The results show that when the tensile strain is induced in the quantum well,the light-hole state becomes the ground state,and the light hole effective masses in the growth direction are strongly reduced while the in-plane effective masses are considerable.Quantitative calculation of the valence intersubband transition between two light hole states in a 7nm tensile strained Si/Si0.55Ge0.45 quantum well grown on a relaxed Si0.5Ge0.5(100) substrates shows a large absorption coefficient of 8400 cm-1.
