Intensity-dependent nonlinearity of the lateral photoconductivity in InGaAs/GaAs dot-chain structures

Abstract

Photoelectric properties of laterally correlated multilayer InGaAs/GaAs quantum dots (QDs) heterostructures are studied. The response of the photocurrent to increasing excitation intensity is found to be nonlinear and varying with excitation energy. The structures are photosensitive in a wide range of photon energies above 0.6 eV. The spectral dependence of the photoconductivity (PC) is caused by strong interaction between the bulk GaAs and the lower energy states of the wetting layer, the QDs, as well as the defect states in the GaAs band gap. In particular, a mechanism for the participation of deep electron trap levels in the photocurrent is clarified. These structures also demonstrate a high sensitivity of up to 10 A/W at low excitation intensities. However, at higher excitation intensities, the sensitivity reduces exhibiting a strong spectral dependence at the same time. The observed sublinear PC dependence on excitation power results from a direct electron-hole recombination both in the QDs and in GaAs host. The solution of rate equations included the contributions of QD ground and exited states, bulk GaAs states and the states of defects within the GaAs bandgap describes well the experimental data.

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

“…3). As well the onset of both the absorption spectra at 0.68 eV, we attribute to the transition from EL2 defect center to the conduction band considering the possible way through the shallow defect levels [24–27, 29]. Similar redshift of EL2-related bands in optical transition have been described for InGaAs/GaAs nanostructures [27, 30].…”

“…As well the onset of both the absorption spectra at 0.68 eV, we attribute to the transition from EL2 defect center to the conduction band considering the possible way through the shallow defect levels [24–27, 29]. Similar redshift of EL2-related bands in optical transition have been described for InGaAs/GaAs nanostructures [27, 30]. However, the fact that no signal below QD spectral band is observed in the PV spectra from only MBE layers means a low amount of EL2-like non-radiative recombination centers in the metamorphic and GaAs buffers overall, providing the effective detection of photocarriers coming from even a single layer of QDs, whereas the high density of recombination centers in the GaAs substrates and n + -GaAs layers of the structures under investigation has been confirmed by the PV characterization of samples measured through the substrate (inset in Fig.…”

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

“…The onset at 0.72 eV is attributed to the transition from the EL2 defect center located in si -GaAs substrate and related interfaces near 0.75 eV below the GaAs conduction band [ 57 ], taking into account the possibility of transition through the shallow levels of defects [ 46 , 54 , 55 ]. The aspects related to their location as well as the EL2 PC onset redshift have been discussed in detail elsewhere [ 10 , 45 ]. As no signal underneath the QD-related bands was observed in the spectra of the samples contacted to the InGaAs or GaAs buffers (Fig.…”

“…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.…”

“…Development of the light-sensitive devices requires in-depth study of the photoelectric properties. Photovoltage (PV) or photoconductivity (PC) studies is an ideal tool for the determination of the photoresponse as function of light energy, transitions between levels, carrier transport, and operating range of the device [ 10 , 43 , 44 ]. However, despite that some studies of the photoelectric properties of structures with metamorphic InAs QDs have been performed in last years [ 37 – 39 , 43 ], full aspects of the photoresponse mechanism still remain unclear, as along with the influence of the MB on the properties of the nanostructures.…”