Influence of growth conditions on the photoluminescence of self-assembled InAs/GaAs quantum dots

We have investigated the influence of various growth parameters on the opti cal properties of self-assembled InAs/GaAs quantum dots (QDs) grown by mole cular beam epitaxy (MBE) in Stranski-Krastanov mode. Metastably sized QDs h ave been observed in photoluminescence measurements, which are fabricated b y depositing 2.5 monolayers (ML) InAs at a substrate temperature of 530 deg rees C and As 4 pressure of (1.6 +/- 0.2) x 10(-5) mbar. These self-assembl ed QDs exhibit both good optical quality and a narrow size distribution wit h a full width at half maximum of similar to 35 meV both at room temperatur e and at 4.2 K. By investigating the dependence of the optical properties o n the substrate temperature and arsenic pressure, we show that the diffusio n length of the adatoms is responsible for changes in size, density, and qu antum efficiency of the QDs beside the amount of InAs deposited. The growth conditions for fabricating QDs are optimized for substrate temperatures T- s = 480 and 530 degrees C. A high QD density (similar to 1 x 10(11) cm(-2)) with a broad size distribution and a lower QD density (similar to 1.2 x 10 (10) cm(-2)) with a narrow size distribution, which are determined by atomi c force microscopy have been obtained by MBE growth at T-s = 480 and 530 de grees C, respectively. Stacking several QD layers separated by thin GaAs sp acers in order to achieve a higher QD density improves the optical properti es of the islands. The thermal stability of the QDs has been tested by anne aling the samples at high temperatures in order to determine the highest po ssible substrate temperature for the following expitaxial layers. The QDs g rown at 530 degrees C can be overgrown at 700-720 degrees C, while the QDs grown at 480 degrees C can only be overgrown at 600-620 degrees C without o bvious decrease of the quantum efficiency of the QDs. (C) 1999 American Ins titute of Physics. [S0021-8979(99)04104- 3].