The spectral sensitivity can further be extended into the longwavelength IR by employing larger HgTe QDs. , corresponding phase plot in the Supporting Information). At room temperature, the device does not exhibit any measurable photoresponse, but a photosignal appears at temperatures below 100 K and gate voltages above zero with a responsivity of about 800 AW -1 (at an applied drain bias of 0.5 V) at a temperature of 80 K which may even increase at lower temperatures and higher applied drain bias. In contrast to commercial IR detectors, the HgTe QD/graphene phototransistor can be fabricated directly on silicon-based substrates, can be repetitively thermally cycled for at least 50 cycles between 300 K and 80 K without device degradation nor failure (Figure ), and pixel pitches below 10 µm are within reach. The soft nature of the QD thin film likely reduces the likelihood of QD film ruptures, and even in the case of a QD film rupture, it would not lead to immediate device failure as photoinduced charge carriers are transported vertically to the graphene interface unaffected by vertical cracks. The photosignal is measured in the electron-conducting regime of graphene (Figure ) and, under illumination, an increase of the current is measured illustrating the transfer of photoinduced electrons from the QD thin film to graphene (Figure , Supporting Information). Based on the similar device architecture of the HgTe QD/graphene phototransistor compared to other QD/graphene phototransistors, we assume a similar device mechanism. The Fermi levels of graphene and the HgTe QD layer align when brought into contact, resulting in a built-in potential as schematically shown in Figure . Under illumination with photon energies above the bandgap, electron-hole pairs are created and, subsequently, the charge carriers are separated at the interface with graphene. Holes are accumulated in the QD film while electrons are transferred to graphene changing the charge carrier conductivity in graphene. After the illumination is switched off, the charge carriers recombine possibly by a temperature-driven Schottky-like potential barrier hopping restoring the steady-state configuration in dark. The photoresponse at low temperatures was observed to be quenched for perovskite QD/graphene phototransistors in a temperature range of 300-200 K. Surprisingly, this is not the case for our HgTe QD/graphene or for PbS QD/graphene phototransistors. Recently, we characterized PbS QD/graphene phototransistors at low temperatures and proposed a temperature-dependent parallel shift of the QD conduction-and valence bands impacting the temperature-dependent performance of the phototransistor. For example, the dependence of the energy levels on QD ligands is known to be reliant on variations of the QD surface dipoles and, so far, reported at a constant temperature. The QD-surface/ligand distance should be temperature-dependent, and therefore, the QD surface dipoles as well, affecting the energy levels of the QD thin film. where BW is the measurement bandwidth, NEP is the noise equivalent power, A is the device area (cm 2 ), R is the responsivity (A W -1 ), in is the noise current (A Hz -1/2 ), and Ids the drain current. The specific detectivity D* is shown in Figure with the highest value of 6×10 Jones at a gate voltage of 6 V, light modulation frequency of 67 Hz, and a wavelength of 2.5 µm. Both the responsivity and noise are strongly dependent on the light modulation frequency as shown in Figure . The measured current-normalized noise-current declines at higher frequencies following a 1/f behavior neglecting the contributions from thermal noise and shot noise (see Noise Contributions in the Experimental Section). The responsivity decreases slowly up to 50 Hz and declines faster beyond 50 Hz, and a 3 dB bandwidth (50 % of the highest responsivity) is reached at 110 Hz. The small differences in the decline of the frequency behavior of the responsivity and noise are more present in Figure . The frequency dependence of the specific detectivity reaches 2.9×10 Jones at a gate voltage of 11 V and a frequency of 45 Hz, and decreases at higher frequencies. While the frequency bandwidth is defined as a 50 % drop in the responsivity value, more attention should be given to the bandwidth of the specific detectivity. Phototransistors exhibit high 1/f noise behavior which compensates the responsivity drop to some extent, while photodiodes have a flat noise behavior and a decrease in responsivity leads to the same decrease in the specific detectivity. Here, 50 % of the maximum specific detectivity is still achieved at 700 Hz and proves that these hybrid HgTe QD/graphene phototransistors can be operated at moderate frequencies at the cost of lower responsivity.