Self-assembled quantum dots for light emitting devices

Karl Eberl

Max-Planck-Institut FKF, Heisenbergstr. 1, 70569 Stuttgart, Germany

Extremely small 10 nm size quantum dots (QD) turn out to be relatively easy to prepare by applying Stranski-Krastanow growth mode in strained layer heteroepitaxie in MBE or CVD. Applications for the self-assembling QD in different material systems are LEDs and laser diodes. For lasers containing QD a lower threshold current density, a higher characteristic temperature, and an increased gain and differential gain in comparison with quantum well lasers are expected due to the discrete energy levels. A further technologically interesting aspect is the access to new emission energies on Si and GaAs substrates.

We provide an overview on the current status of research in the field and present latest results especially on red light emitting InP/AlGaInP laser diodes on GaAs substrate. They contain densely stacked layers of InP QD embedded in Ga0.51In0.49P waveguide layers. The edge emitting diodes show quantum dot ground state lasing in the visible part of the spectrum (690 - 705 nm).

In addition we report about preparation and optical properties of self-assembling Ge QD in Si. Si and Ge are indirect semiconductors, consequently the emission involves phonon assistance which makes radiative recombination inefficient. Due to strong carrier confinement in extremely small QD momentum conservation becomes relaxed. This results in substantially increased optical emission in the range from 1.3 to 1.55Ám from stacked Ge QD on Si substrate.