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

Abstract

The bipolar effect of GaAs substrate and nearby layers on photovoltage of vertical metamorphic InAs/InGaAs in comparison with pseudomorphic (conventional) InAs/GaAs quantum dot (QD) structures were studied. Both metamorphic and pseudomorphic structures were grown by molecular beam epitaxy, using bottom contacts at either the grown n +-buffers or the GaAs substrate. The features related to QDs, wetting layers, and buffers have been identified in the photoelectric spectra of both the buffer-contacted structures, whereas the spectra of substrate-contacted samples showed the additional onset attributed to EL2 defect centers. The substrate-contacted samples demonstrated bipolar photovoltage; this was suggested to take place as a result of the competition between components related to QDs and their cladding layers with the substrate-related defects and deepest grown layer. No direct substrate effects were found in the spectra of the buffer-contacted structures. However, a notable negative influence of the n +-GaAs buffer layer on the photovoltage and photoconductivity signal was observed in the InAs/InGaAs structure. Analyzing the obtained results and the performed calculations, we have been able to provide insights on the design of metamorphic QD structures, which can be useful for the development of novel efficient photonic devices.

Interband Photoconductivity of Metamorphic InAs/InGaAs Quantum Dots in the 1.3–1.55-μm Window

“…However, it is noteworthy that an increase in photon energy above ε g leads to a slight decrease of the photoresponse. Naturally, this confirms that metamorphic QDs, despite being effective recombination centers [ 1 , 2 , 12 , 22 ], are more efficient contributors to photocurrent than MB [ 5 , 6 , 23 ].…”

“…The shift is related to the reduction of the lattice mismatch between the materials of InAs QD and In x Ga 1 − x As buffer with an increase in x and, hence, a decrease in the strain in QDs. This leads to a narrowing of the InAs QD bandgap and, in turn, to the redshift of the PL band as well as the photoresponse onset toward IR [ 1 – 6 , 19 , 35 ].…”

“…The key role for the development of this area is the preservation of a high emission efficiency and photosensitivity of metamorphic QD structures that need to be at least comparable with those of conventional InAs/GaAs QD structures [ 1 , 5 , 35 ]. A lot of studies were carried out in the fundamental and application fields to develop structure design [ 6 , 14 , 21 ], to improve photoelectric properties [ 5 , 13 ], and to control/reduce strain-related defects in the heterostructures [ 4 , 36 , 37 ].…”

Defect influence on in-plane photocurrent of InAs/InGaAs quantum dot array: long-term electron trapping and Coulomb screening

“…At higher energies, simultaneous transitions in WL and buffers occur (In x Ga 1-x As MB E g are shown in figure 2). However, the buffer-related component can also originate from the transitions between band and shallow defect levels located in the MB, that was reported to be the reason for this component onset redshift in similar samples [37][38][39]. The PC signal at the energies below the PL band edges could be related to the defects detected earlier, EL2-like (E c -0.74 eV) and ED1 (E c -0.52-0.54) [36,42].…”

“…Also, significant efforts in optimizing the structure design were carried on to avoid the influence on PC of the substrate and of nearby layers with interface defects [37]. Utilizing the new design, we compared the photoelectric properties of a metamorphic InAs/In 0.15 Ga 0.85 As QD structure with those of a standard InAs/GaAs QD one; this allowed to conclude about efficient light sensing by the metamorphic QDs [38,39]. However, we expect that, independently on the particular design used, PC should be affected by levels related to defects in the vicinity of QD layers.…”