A number of research efforts have been focused on self-assembled germanium quantum dots in which indirect optical transitions take place across the band gap. However, many quaestions regarding the confined electronic state transitions of Ge quantum dots still remain unanswered. In the present report, we have depolsited ten alternating layers ofcrystalline Ge quantum dots embedded in an Al_2O_3 or an AlN matrix on sapphire substrates by pulsed laser deposition. The average dot sizes (73 A to 260 A) were controlled by the laser energy density, deposition time and substrate temperature. The spectral positions of both the E_1 and the E_2 transitions in the absorption spectra at room temperature and 77K shift toward higher energy ( DELTA EA_1 chemical bounds 1.19 eV, DELTA E_2 chemical bounds 0.57 eV) as the Ge dot size dcreases (73 A). Structural analysis using transmission electron microscopy and atomic force microscopy and the interpretation of optical absorption measurements in terms of quantum confinement of carrriers in both transition are presented.
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