Comparative Study of Photoelectric Properties of Metamorphic InAs/InGaAs and InAs/GaAs Quantum Dot Structures

Abstract

Optical and photoelectric properties of metamorphic InAs/InGaAs and conventional pseudomorphic InAs/GaAs quantum dot (QD) structures were studied. We used two different electrical contact configurations that allowed us to have the current flow (i) only through QDs and embedding layers and (ii) through all the structure, including the GaAs substrate (wafer). Different optical transitions between states of QDs, wetting layers, GaAs or InGaAs buffers, and defect-related centers were studied by means of photovoltage (PV), photoconductivity (PC), photoluminescence (PL), and absorption spectroscopies. It was shown that the use of the InGaAs buffer spectrally shifted the maximum of the QD PL band to 1.3 μm (telecommunication range) without a decrease in the yield. Photosensitivity for the metamorphic QDs was found to be higher than that in GaAs buffer while the photoresponses for both metamorphic and pseudomorphic buffer layers were similar. The mechanisms of PV and PC were discussed for both structures. The dissimilarities in properties of the studied structures are explained in terms of the different design. A critical influence of the defects on the photoelectrical properties of both structures was observed in the spectral range from 0.68 to 1.0 eV for contact configuration (ii), i.e., in the case of electrically active GaAs wafer. No effect of such defects on the photoelectric spectra was found for configuration (i), when the structures were contacted to the top and bottom buffers; only a 0.83 eV feature was observed in the photocurrent spectrum of pseudomorphic structure and interpreted to be related to defects close to InAs/GaAs QDs.

Bipolar Effects in Photovoltage of Metamorphic InAs/InGaAs/GaAs Quantum Dot Heterostructures: Characterization and Design Solutions for Light-Sensitive Devices

“…1 . By analysis of AFM data on similar structures, most frequent values of QD sizes were estimated to be 20 nm (diameter) and 4.9 nm (height) for metamorphic QDs and 21 nm (diameter) and 5.0 nm (height) for standard QDs [ 30 , 31 , 45 ].…”

“…The calculation of QD quantum levels is out of the scope of this paper, and QD modeling has been performed previously in Ref. [ 45 ]. In this work, however, we calculate band profiles of the whole heterostructure including the substrate.…”

“…Vertical photocurrent and PV spectra were measured in the 0.6 to 1.8 eV range using normal incidence excitation geometry at room temperature (RT) (300 K) and same light source intensity (1.5 mW/cm 2 ). The photocurrent was measured using a current amplifier and direct current technique [ 10 , 43 – 45 ], with 1 V bias. The current was measured as a voltage signal drop across a series load resistance of 100 kΩ (see the inset in Fig.…”

“…Thus, while the applied contact geometry is to retain the bottom layers and substrate electrically inactive, a notable negative effect of them on PV and photocurrent has been detected by us in a previous investigation [ 43 ]. Very recently, we compared the photoelectric properties of the metamorphic InAs/In 0.15 Ga 0.85 As QD structure with those of a standard InAs/GaAs QD one and found that the photocurrent of metamorphic InAs/In 0.15 Ga 0.85 As heterostructures was not affected by levels related to defects in the vicinity of QD [ 45 ]. Furthermore, it has been concluded that efficient photonic devices at 1.3 μm can be developed with similar nanostructures as an active material.…”

Optical windows for head tissues in near‐infrared and short‐wave infrared regions: Approaching transcranial light applications

“…Being encouraged by a rapid progress in the development of new NIR‐SWIR sensitive cameras based on InGaAs or InSb photodetectors and new laser sources , the use of NIR‐SWIR light for in vivo applications (ie, optical imaging and therapy) are being actively advanced. These windows allow researchers to benefit from the reduced tissue scattering and autofluorescence in these spectral regions and achieve deeper light penetration .…”