Monolithically Integrated InAs/GaAs Quantum Dot Mid-Infrared Photodetectors on Silicon Substrates

High-performance, multispectral, and large-format infrared focal plane arrays are the long-demanded third-generation infrared technique for hyperspectral imaging, infrared spectroscopy, and target identification. A promising solution is to monolithically integrate infrared photodetectors on a silicon platform, which offers not only low-cost but high-resolution focal plane arrays by taking advantage of the well-established Si-based readout integrated circuits. Here, we report the first InAs/GaAs quantum dot (QD) infrared photodetectors monolithically integrated on silicon substrates by molecular beam epitaxy. The III–V photodetectors are directly grown on silicon substrates by using a GaAs buffer, which reduces the threading dislocation density to ∼106 cm–2. The high-quality QDs grown on Si substrates have led to long photocarrier relaxation time and low dark current density. Mid-infrared photodetection up to ∼8 μm is also achieved at 80 K. This work demonstrates that III–V photodetectors can directly be integrated with silicon readout circuitry for realizing large-format focal plane arrays as well as mid-infrared photonics in silicon

AlP/GaP quantum wells for implementing intersubband devices in the 30-60 µm wavelength region.

International audienc

Excitation correlation photoluminescence in the presence of Shockley Read Hall recombination

Excitation correlation photoluminescence ECPL measurements are often analyzed in the approximation of a cross correlation of charge carrier populations generated by the two delayed pulses. In semiconductors, this approach is valid for a linear non radiative recombination path, but not for a non linear recombination rate as in the general Shockley Read Hall recombination scenario. Here, the evolution of the ECPL signal was studied for deep trap recombination following Shockley Read Hall statistics. Analytic solutions can be obtained for a fast minority trapping regime and steady state recombination. For the steady state case, our results show that the quadratic radiative term plays only a minor role, and that the shape of the measured signal is mostly determined by the non linearity of the recombination itself. We find that measurements with unbalanced intense pump and probe pulses can directly provide information about the dominant non radiative recombination mechanism. The signal traces follow the charge carrier concentrations, despite the complex origins of the signal, thus showing that ECPL can be applied to study charge carrier dynamics in semiconductors without requiring elaborate calculations. The model is compared with measurements on a reference sample with alternating layers of InGaAs InAlAs that were additionally cross checked with time resolved optical pump terahertz probe measurements and found to be in excellent agreemen

Band offsets of InGaP/GaAs heterojunctions by scanning tunneling spectroscopy

Scanning tunneling microscopy and spectroscopy are used to study InGaP/GaAs heterojunctions with InGaAs-like interfaces. Band offsets are probed using conductance spectra, with tip-induced band bending accounted for using three-dimensional electrostatic potential simulations together with a planar computation of the tunnel current. Curve fitting of theory to experiment is performed. Using an InGaP band gap of 1.90 eV, which is appropriate to the disordered InGaP alloy, a valence band offset of 0.38±0.01 eV is deduced along with the corresponding conduction band offset of 0.10±0.01 eV (type I band alignment)

Iron doped InGaAs: Competitive THz emitters and detectors fabricated from the same photoconductor

Today, the optimum material systems for photoconductive emitters and receivers are different. In THz reflection measurements, this leads to complicated optics or performance compromises. We present photoconductive emitters and detectors fabricated from molecular beam epitaxy (MBE) grown iron (Fe) doped InGaAs, which are well suited for a THz time-domain spectroscopy as both emitters and detectors. As a photoconductive emitter, 75 mu W +/- 5 mu W of radiated THz power was measured. As a detector, THz pulses with a bandwidth of up to 6 THz and a peak dynamic range of 95 dB could be detected. These results are comparable to state-of-the-art THz photoconductors, which allows for simple reflection measurements without a performance decrease. The incorporation of Fe in InGaAs during MBE growth is investigated by secondary ion mass spectroscopy, Hall, and transient differential transmission measurements. Growth temperatures close to 400 degrees C allow for homogeneous Fe doping concentrations up to 5 x 10(20) cm(-3) and result in a photoconductor with an electron lifetime of 0.3 ps, a resistivity of 2 k Omega cm, and an electron mobility higher than 900 cm(2) V-1 s(-1). We show that iron dopants are incorporated up to a maximum concentration of 1 x 10(17) cm(-3) into substitutional lattice sites. The remaining dopants are electrically inactive and form defects that are anneal-stable up to a temperature of 600 degrees C. The fast recombination center in Fe-doped InGaAs is an unidentified defect, representing approximate to 0.5% of the nominal iron concentration. The electron and hole capture cross section of this defect is determined as sigma(e) = 3.8 x 10(-14) cm(2) and sigma(h) = 5.5 x 10(-15) cm(2), respectively

Concept and demonstration of an intermediate band tandem device for solar energy conversion

We have realized a tandem solar cell design that combines a pin junction with a photovoltaic intersubband absorber. This concept allows harvesting light in the visible range and the near and mid infrared at the same time, and theoretically, energy conversion efficiencies beyond the Shockley Queisser limit could be achieved. A test structure was grown, and the operation of this concept could be confirmed, in principal with an optical two beam experiment. The basic characteristics of the device can be explained with an equivalent circuit design that consists of three individual cells, and we find an obvious analogy to the concept of the intermediate band solar cell with noteworthy advantages at some points. Our results show, that for a working device it is crucial to adjust the properties of the photovoltaic intersubband absorber for optimal charge separating performance at the working point of the solar cel