Experimentally, T BLIP can be estimated

from comparing the dark current curves with the photocurrent characteristics obtained by allowing the 300-K radiation through the Dewar window [1]. In Figure 2, we can see that the current from the background radiation is equal to the dark current at 100 K and negative bias. This temperature is higher than that measured for Ge/Si QDIP [13] and GeSi/Si QWIP [17] operating in long-wave IR region and exceeds T BLIP found for many n-type InAs QD-based GSI-IX detectors [18–21]. Figure SN-38 order 2 The bias dependence of dark current measured at temperatures from 80 to 120 K. The dashed line represents the response to a 300-K background radiation through the Dewar window (field of view = 53°). BLIP prevails at 100 K for negative

bias voltage. Figure 3 shows the normal incidence spectral response at 90 K for different bias voltages. At zero bias, no signal is observed implying the device operates in a photoconductive mode [22], and at biases just above 3.5 V, the signal becomes too noisy to detect PC. Ge/SiGe QDIP is of wide detection window with the cutoff wavelength of about 12 μm instead of 5 to 6 μm for Ge/Si QDIPs of similar device structure [11]. Since the sample in FTIR experiments is simultaneously exposed to a wide range of photon energies, the spectra may display additional transitions due to two-photon processes [9]. The near-infrared photons with energies larger than the SiGe bandgap create electrons and holes mostly in the SiGe barrier. The nonequilibrium holes diffuse from the SiGe bulk www.selleckchem.com/products/eft-508.html towards the Ge QDs and are accumulated in the dots. Then, by absorbing the mid-infrared photons, the photoexcited holes may contribute to the mid-infrared

PC. To check this assumption, a 2.5- μm optical low-pass filter was introduced in front of the sample to eliminate the photons which may cause band-to-band transitions in the Si and SiGe layers. The long-wave part of the photoresponse remains unchanged. Thus, we conclude that 3-mercaptopyruvate sulfurtransferase the observed redshift is a result of smaller effective valence band offset at the Ge/Si 1−x Ge x interface. By an analogy with the behavior of Ge/Si QDIPs [11], the near-infrared response at λ<2 μm is ascribed to the interband transitions between the electrons in the δ valleys of SiGe layers and the holes at the Γ point of Ge QDs. The mid-infrared signal at λ>3 μm is associated with the hole intraband transitions which involve the dot bound states. Figure 3 Responsivity spectra under different applied biases of Ge/SiGe QDIP. The applied voltages are ±0.05, ±0.1, ±0.5, ±1.0, ±1.5, ±2.0, ±2.5, and −3.0 V. The sample temperature is 90 K. The bias voltage dependence of the relative photoresponse R long/R mid is plotted in Figure 4a, where R long is the PC integrated over the long-wave window from 8 to 12 μm, and R mid is the integral response in the mid-wave region from 3 to 5 μm.