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The dark current of Quantum Well Inter-subband Photodetectors is affected by 1/f noise that limits the detectivity. This paper applies for the first time conventional quantum 1/f noise expressions to calculate the expected level of 1/f noise in QWIPs and applies the resulting engineering formulas to the case of GaInAs/InP and GaN/AlGaN QWIPs. Both the collisionless and collision-dominated cases are considered. The elementary process causing the dark current is the transfer of an electron from one well to the neighboring well. This happens under the influence of the applied electric field, and has in general both thermally activated and tunneling components. The larger the applied electric field, the larger is the squared velocity change of the carriers, and the larger is the obtained conventional quantum 1/f effect. The detectivity of the devices is calculated on this basis. Quantum well intersubband photodetectors (QWIPs) can be extended in principle from infrared into the THz region.

GaN-based FETs, HFETs and MODFETs are ideally suited for use in high-power amplifiers and oscillators, due to their large band gap and high operating voltages. According to the quantum 1/f theory, the larger effective mass implied for the carriers also leads to lower fundamental 1/f noise and to lower resulting phase noise close to the carrier frequency. We have therefore studied the quantum 1/f noise sources in the channel and in the gate insulation. For the channel, a combination of conventional and coherent Quantum 1/f Effect (Q1/fE) is present, with the conventional Q1/fE dominant in the sub-threshold part of the channel toward the drain. It turns out that the quantum 1/f parameter "s" that determines the fraction of the two forms of Q1/fE, is no longer increasing proportionally to the width of the device w, when the latter exceeds the length of the channel. A logarithmic dependence on w is obtained for s instead. This is why an extremely large width w does not automatically lead to coherent Q1/fE in HFETs. Conventional Q1/fE applies for the gate insulation, with contributions of the much larger piezoelectric Q1/fE in spontaneously polarized AlGaN, if gate leakage is present. The noise figure is calculated, including all contributions. Finally, the minimal expected oscillator phase noise is calculated from the Q1/fE in the dissipative elements, even for perfectly linear amplifiers, by multiplication with the inverse fourth power of the quality factor, as was first done by us for quartz in 1979.

For imaging and remote sensing applications, the noise of the THz detector must be minimized. The quantum 1/f theory is introduced and used to obtain analytical expressions of noise in n + p diodes, Schottky diode THz detectors and mixers, a new type of suggested MEMS resonator based Thz detectors, QWIPs and bolometers. For the DAR and for THz communications we also consider phase noise in RTD and GaN/AlGaN HFET based THz generators.