Low frequency noise sources in InAlAs/InGaAs MODFETs

Detailed analysis of the 1/f low-frequency noise (LFN) in In_0.52Al_0.48As/InGaAs MODFET structures is performed, for low drain bias (below pinch-off voltage), in order to identify the physical origin and the location of the noise sources responsible for drain current fluctuations in the frequency range 0.1 Hz-10⁵ Hz. Experimental data were analyzed with the support of a general modeling of the 1/f LFN induced by traps distributed within the different layers and interfaces which constitute the heterostructures. Comparative noise measurements are performed on a variety of structures with different barrier (InAIAs, InP) and different channel (InGaAs lattice matched to InP, strained InGaAs, InP) materials. It is concluded that the dominant low frequency noise sources of InAlAs/InGaAs MODFET transistors in the ON state are generated by deep traps distributed within the "bulk" InAlAs barrier and buffer layers. For reverse gate bias, the gate current appears to be the dominant contribution to the channel LFN, whereas both the gate current and the drain and source ohmic contacts are the dominant sources of noise when the device is biased strongly in the ON state. Heterojunction FET\´s on InP substrate with InP barrier and buffer layers show significantly lower LFN and appear to be more suitable for applications such as nonlinear circuits that have noise upconversion.