AsN3138 is almost identical to AsN3134 but with 20 QWs. In all samples, the wells are separated from each other by wide GaAs barriers. The samples were fabricated in the shape of a mesa structure, with a top circular aperture of 1 mm diameter. Further details about structure, growth parameters and fabrication process can be found elsewhere [19]. Table 1 Samples’ key TGF-beta activation structure parameters together with the RT PL peak wavelength Sample No. QWs QW thickness (nm) x and y (%) Structure RT PL peak λ (nm) AsN2604 10 3.8 to 11 4 and 1.5 p-i-n 1,033 AsN3134 10 10 4.8 and 1.6 p-i-n 1,067 AsN3138 20 10 4.8 and 1.6 p-i-n 1,077 VN1585 10 10 3 and 1 n-i-p 998 Optical quality of the devices

was determined using CW photoluminescence (PL) as a function of temperature. Table 1 lists the room temperature (RT) GaInNAs PL peak wavelengths. The p-n junction quality

was determined buy BI 2536 by measuring the current–voltage characteristic in the growth direction, in darkness, in the forward and reverse bias configurations. The measurements were carried out over the temperature range between T = 15 K and 300 K. Photocurrent oscillations were also carried out at the same temperature range when the samples were illuminated using a 950-nm LED. Spectral photoresponse was measured by uniformly CB-839 illuminating the samples with variable wavelength monochromatic light. Results and discussion Figure 1 shows the photocurrent versus voltage characteristics for sample VN1585 at temperatures between T = 40 K and 200 K. At T > 140 K, the curves are smooth at all the applied bias voltages. At T = 140 K, a number of small discrete steps appear, and at around T approximately 120 K, these steps are clearly visible and get increasingly more pronounced with decreasing temperature. The first derivatives of the I-V curves are plotted in the top left inset in Figure 1. It is clear that the steps in the photocurrent correspond to well-defined oscillations in the dI/dV curves. The number of the oscillations, DNA ligase 10, is the same as the number of QWs in the

sample. The amplitude of each oscillation has the temperature dependence as shown in the bottom inset in Figure 1. All the samples studied showed similar behaviour to that in VN1585. Figure 1 VN1585 temperature-dependent I – V under illumination. The top left inset shows the derivative of the I-V curves, while the right bottom one shows the oscillations’ amplitude as a function of temperature. In order to establish whether the oscillations are associated with optically excited carriers in the GaInNAs QWs, the spectral dependence of the photocurrent were measured. The spectral response of AsN2604 (Figure 2) increases with increasing wavelength but cuts off at a wavelength of 830 nm corresponding to the GaAs bandgap.