Microwave mixing and noise measurement techniques have been used to characterize energy relaxation and noise phenomena for the two-dimensional electron gas (2DEG) medium in single AlGaAs/GaAs modulation-doped quantum wells. Mixing experiments at 94 GHz yield the energy relaxation time directly, in good agreement with optical methods previously reported. The noise output power at low microwave frequencies (1.5–3.5 GHz), is shown to have one term due to Nyquist noise at the electron temperature, and a second frequency-dependent term caused by fluctuations in the electron temperature.
This paper presents a new type of electron bolometric ("hot electron") mixer. We have demonstrated a three order of magnitude improvement in the bandwidth compared with previously known types of electron bolometric mixers, by using the two-dimensional electron gas (2DEG) medium at the hetero-interface between AlGaAs and GaAs. We have tested both in-house MOCVD-grown material, and MBE material, with similar results. The conversion loss (L ,) at 94 GHz is presently 18 dB for a mixer operating at 20 K, and calculations indicate that L, can be decreased to about 10 dB in future devices. Calculated and measured curves of L, versus &o, and IDC, respectively, agree well. We argue that there are several different configurations of electron bolometric mixers, which will all show wide bandwidth, and that these devices are likely to become important as low-noise THz receivers in the future.
This paper describes a research effort, supported by the NASA Innovative Research Program, aimed at developing new types of THz low noise receivers, based on bulk effect ("hot electron") nonlinearities in the Two-Dimensional Electron Gas (2DEG) Medium, and the inclusion of such receivers in focal plane arrays. The original motivation and objectives of the research are discussed at some length. The results obtained cover several different sub-areas, and are discussed briefly, with references to other more detailed publications. 2DEG mixers have been demonstrated at 35 and 94 GHz with three orders of magnitude wider bandwidth than previous hot electron mixers. These mixers employ a new mode of operation, which was invented during this program. Based on the results of this research, it is now possible to design a bulk effect mixer focal plane array for the THz range, which is anticipated to have a DSB receiver noise temperature of 500-1000 K.
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