Si/Ge Nano Optoelectronic Device

This thesis mainly focuses on Ge quantum dots (QDs) grown by ultra high vacuum chemical vapor deposition (UHVCVD). We have archived a density higher than 1011 cm-2 with informal QDs about 10%. We also have successfully fabricated optoelectronic devices by use of self-organized Ge QD nano structure. Different methods are designed to reduce the dark current for the devices grown with CVD and MBE respectively.
In quantum dot infrared photodetector (QDIP) fabricated by MBE, we have demonstrated a QDIP in our preliminary work on Ge QDs devices. In IR responsivity, our QDIPs have a very broad and tunable spectrum in the range 1.6~20 μm under applied biases. The maximum single wavelength detectivity of our devices is about 2.1x1010 cm (Hz0.5)/W under 0.2 V for 6 μm wavelength radiation at 30K. According to the current-voltage characteristics, the background limited performance can reach 50 K.
In QDIP grown by UHVCVD, we report the growth of a high quality 20-period perfectly vertically aligned Ge/Si multiple quantum dots with the structure of the metal-semiconductor Schottky barrier to reduce the dark current. In IR responsivity, our QDIPs show two groups of broad spectra in 2~4.5μm and 4.5~9μm at low temperature. They come from Ge QDs and wetting layers respectively. The response of wetting layers vanishes above 90K while the response of Ge QDs vanishes above 150K. For the samples we present in the thesis, the maximum detectivity at 30K under +0.5V is 7.3 × 109 cmHz0.5/W. The current-voltage characteristic shows that the dark current is reduced by the Schottky barrier so that the detector can be applied in higher temperature for the thermal image detection.
In QD LEDs, we compared the experimental results of devices with different fold number of Ge quantum dots. By analyzing these results, we found the influence of stacking quantum-dot layers on electroluminescence spectra and other characteristics. A possible mechanism based on the temperature-dependent minority carrier electron diffusion length was also proposed to explain some of these influences, especially the temperature-dependence of EL spectra of the devices with various fold number.
The optoelectronic devices based on nano Ge QDs have been demonstrated. According to our results, the Ge QDIPs with Schottky barrier as a dark current blocker show the thermal image capability for high working temperature. The carrier dynamic in the QD LEDs have been analyzed. Due to the property of Ge QD and p-i-n device structure, we found the intensity enhancement with temperature. This behavior may be the key for the light emission form Si based device. The 1.55μm operating wavelength also shows the possibility that nano Ge QDs can communicate with fiber. Summarizing our experimental results, the nano Ge QDs is a way leads to the OEICs with Si based technology.