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.

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- μm and 8- to 12- μm 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 μm 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 μm 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.