Anatolii Dvurechenskii

Broadband Ge/SiGe quantum dot photodetector on pseudosubstrate

We report the fabrication and characterization of a ten-period Ge quantum dot photodetector grown on SiGe pseudosubstrate. The detector exhibits tunable photoresponse in both 3- to 5- μ m and 8- to 12- μ m spectral regions with responsivity values up to about 1 mA/W at a bias of −3 V and operates under normal incidence radiation with background limited performance at 100 K. The relative response in the mid- and long-wave atmospheric windows could be controlled through the applied voltage.

Photovoltaic Ge/Si quantum dot detectors operating in the mid-wave atmospheric window (3 to 5 μm)

Ge/Si quantum dots fabricated by molecular-beam epitaxy at 500°C are overgrown with Si at different temperatures Tcap, and effect of boron delta doping of Si barriers on the mid-infrared photoresponse was investigated. The photocurrent maximum shifts from 2.3 to 3.9 μ m with increasing Tcapfrom 300°C to 750°C. Within the sample set, we examined devices with different positions of the δ-doping layer with respect to the dot plane, different distances between the δ-doping layer and the dot plane d, and different doping densities pB. All detectors show pronounced photovoltaic behavior implying the presence of an internal inversion asymmetry due to the placing dopants in the barriers. The best performance was achieved for the device with Tcap = 600°C, pB = 12 × 1011cm−2, and d = 5 nm in a photovoltaic regime. At a sample temperature of 90 K and no applied bias, a responsivity of 0.83 mA/W and detectivity of 8 × 1010 cm Hz1/2/W at λ = 3.4 μ m were measured under normal incidence infrared radiation.

Electromodulated reflectance study of self-assembled Ge/Si quantum dots

We perform an electroreflectance spectroscopy of Ge/Si self-assembled quantum dots in the near-infrared and in the mid-infrared spectral range. Up to three optical transitions are observed. The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band. The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and Δ(4) valleys of the Ge conduction band, and the localized hole states at the Γ point.

GERMANIUM SELF-ASSEMBLED QUANTUM DOTS IN SILICON FOR MID-INFRARED PHOTODETECTORS

We present an overview of the experimental results in the field of quantum dot infrared photodetectors (QDIPs) implemented on Ge self-assembled quantum dots (QDs) in Si. QDs are fabricated using Stranski-Krastanov epitaxial growth mode. The effect of photoconductivity is associated with the photoexciation of holes from bound to bound states in Ge QDs or from bound states in Ge dots to continuum states in the Ge wetting and Si barrier layers. The depolarization field effect in the collective interlevel excitations of a dense array of Ge/Si QDs is discussed. The comparison between operating characteristics of QDIPs based on III–V and Ge/Si heterostructures is included.

Influence of delta-doping on the hole capture probability in Ge/Si quantum dot mid-infrared photodetectors

We study the effect of delta-doping on the hole capture probability in ten-period p-type Ge quantum dot photodetectors. The boron concentration in the delta-doping layers is varied by either passivation of a sample in a hydrogen plasma or by direct doping during the molecular beam epitaxy. The devices with a lower doping density is found to exhibit a lower capture probability and a higher photoconductive gain. The most pronounced change in the trapping characteristics upon doping is observed at a negative bias polarity when the photoexcited holes move toward the δ-doping plane. The latter result implies that the δ-doping layers are directly involved in the processes of hole capture by the quantum dots.

Determination Of Quantum Dots Structural Parameters By XAFS Spectroscopy

Surface sensitive XAFS (X‐ray absorption fine structure) measurements based on total electron yield and fluorescence yield detection modes have been performed for pseudomorphous Ge films and clusters deposited on Si(001) and Si(111) substrate via molecular beam epitaxy (MBE). Deposited Ge islands reveal quantum dots (QD) properties. The influence of Ge nanoislands sizes and shape, Si substrate orientation and pretreatment, and MBE deposition conditions on the QD microstructure parameters are studied. The local microstructure parameters are linked to heterostructures morphology. Adequate models of spatial structure are suggested and discussed. The appearance of free levels at a depth of the order of 0.4 eV from the top of the Ge valency band for the containing QD samples doped with boron is revealed.

Hole transport in Ge/Si quantum-dot field-effect transistors

We report on the transport properties of Si field-effect transistors with an array of approximately 103 10-nm-diameter Ge self-assembled quantum dots embedded into the active channel. The drain current versus gate voltage characteristics show oscillations caused by Coulomb interaction of holes in the fourfold-degenerate excited state of the dots even at room temperature. A dot charging energy of approximately 43 meV (i.e., > kT = 26 meV at T = 300 K) and disorder energy of approximately 20 meV are determined from the oscillation period ad the temperature dependence sudy of current maxima, respectively.