Low-frequency noise in barrier-gate FET 3P326

In order to construct barrier-gate FET low-noise microwave devices, one needs data on the intensities of primary noise sources acting in the latter. The noise source intensities are related in the simplest manner to fluctuations of the drain current of a statically operating transistor. This relation has been shown in the analysis performed in [I]. Concentration fluctuations in passive near-contact channel regions have been shown, in particular, to contribute to the barrier-gate FET drain current noises for low-drain voltage U d and gate voltage Ug. Current noises are defined almost entirely by concentration fluctuations in the active channel portion for the drain voltages which correspond to volt-ampere characteristic saturation and low gate voltages. Barrier-gate FET noises are observed to result, for large drain and gate voltages, from fluctuations in the number of charged centers in a depletion under-gate region. A number of 3P326 type transistors were studied in this paper whose purpose is to obtain information on the noise sources. Typical transistor volt- ampere characteristics are depicted in Fig. 1. Energy spectra of relative transistor drain current noises Si(F) are depicted in Figs. 2-4 for different drain and gate voltages. The sensitivity level of an experimental plant is shown by dotted lines in the figures. The relative error of noise measurements was below 1.5 dB. Transistor current noise levels measured for low-drain voltages U d = 0.2-0.3 V and uf = 0 were found to differ by at most 10-13 dB in the studied frequency range F = 0.3-2.104 Hz (Fig. 2). The spectra have a typical form. It can be considered as a result of superposition of generation-recombination processes with a certain distribution of relaxation times r and is described by the expression [2] where the minimum time constant is r 0 = 1/F = 10-2-10 -1 sec in the case studied. The small scatter of transistor noise levels in this regime is indicative of approximately the same quality of reference semiconductor material and drain and source contacts used. As the drain voltage increases up to 1-1.5 V, the relative noise level is observed to increase by 3-5 dB (Fig. 3). The spectra form is observed to remain the same, on the whole. No. 34 barrier gate FET is an exception whose spectrum acquires the form Si(F ) - F ~ A specific feature of this transistor is the increased gate leakage current, which amounts to 1/~A for U d = 1 V, Ug = 0. Increase in the gate voltage up to a value corresponding to one-half of the cutoff voltage results in an increase in the relative noise level S i by 10 dB, on the average (Fig. 4), as compared with the case of Ug = 0. The increase amounts to 15-17 dB in No. 19 barrier-gate FET exhibiting low noise for Ug = 0, while it is only 3-10 dB for a high-noise No. 43 barrier-gate FET. The difference in the noise level of the transistors studied was observed to reach 23 dB at a frequency F = 100 Hz. The form of the spectra Si(F) differed from that observed for Ug = 0. The generation-recombination-component appeared at a frequency F = 10 kHz and the spectrum bend was observed to disappear at frequencies F = 10-100 Hz in the majority of the transistors. The noise level of an anomalous barrier-gate FET No. 34 is observed to increase by 10 dB with no change in the form of the spectrum. A spectrum close to the latter is acquired by current fluctuations in the No. 37 transistor which exhibited the same characteristics for other U d, Ug. The large scatter in the current noise level in this regime in a barrier-gate FET indicates that there is a pronounced difference in the quality of the gate areas of the transistors investigated. *Presented at the All-Union Coordination Conference "Low-Frequency Noise in Semiconductor Instruments and Devices"