We have investigated the device characteristics of quantum dot infrared photo detector (QDIP) utilizing InAs QDs in an In0.15Ga0.85As quantum well structure. Device characteristics, such as dark current, photoluminescence (PL), and photocurrent spectra, have been measured. Two peak positions were measured at 163 and 219 meV in photocurrent spectrum. The photo-current of the peak at 163 meV was larger than that at 219 meV. The full width at half maximum (FWHM) of the peak at 163 meV was 18 meV, which was attributed to bound-to-bound transition. In0.15Ga0.85As layers were believed to contribute to induce bound-to-bound transition energy (163 meV). The activation energies of electrons in an InGaAs QDs were determined to be 171 meV and 221 meV from temperature-dependent integrated PL intensities. These activation energies from PL measurement are quite well matched to peak IR detection energies of 163 meV and 219 meV from the photo-current spectrum. This result implies that one can estimate the peak IR detection wavelength of QDIP from PL measurements of QDIP structure before its fabrication and measurement.
In this study, we have studied the thermal treatment effect not only on the optical and structural properties of QDIP structure but also device performance of the QDIP. The thermal treatment of InAs/GaAs QDIP structure have been carried out at the temperature range from 650oC and 850oC with SiO2 capping layer for 1 minute under the N2-gas ambient. After the thermal treatment, the structure was processed to QDIP and its device characteristics such as dark current and IR photo-response were measured. Results show that the photoluminescence (PL) peak was blue-shifted from 1288nm to 1167nm while the peak of photo-currents spectrum was red-shifted from 7.6 um to 7.8 um after the thermal treatment. It is also noted that the thermally treated sample showed the increase of photo-currents, which resulted in the increase of detectivity.
Intermixing effects of MOCVD (metal organic chemical vapor deposition) grown InGaAs SAQDs (self-assembled quantum dots) covered with SiO2 and SiNx-SiO2 dielectric capping layers were investigated. The intermixing of SAQDs was isothermally performed at 700°C by varying annealing time under the N2-gas ambient. It was confirmed from the PL measurement after the thermal annealing that, the emission energy of SAQDs was blue-shifted by 190 meV, the FWHM (full width at half maximum) was narrowed from 76 meV to 47 meV and the PL intensity was increased. SiNx-SiO2 double capping layer have been found to induce larger PL intensity after the thermal annealing of SAQDs compared to SiO2 single capping layer. The results can be implemented for increasing quantum efficiency and tuning the detection wavelength in quantum dot infrared photodetector (QDIP).