Fundamentals of Tunnel Field-Effect Transistors by Saurabh Sneh; Kumar Mamidala Jagadesh;

Fundamentals of Tunnel Field-Effect Transistors by Saurabh Sneh; Kumar Mamidala Jagadesh;

Author:Saurabh, Sneh; Kumar, Mamidala Jagadesh;
Language: eng
Format: epub
Publisher: CRC Press


FIGURE 5.8

Heterojunction In0.7Ga0.3As TFETs with different structure of the tunneling junction [9].

5.9 Impact of Temperature

FIGURE 5.9

Qualitative comparison of transfer characteristics of a TFET at T = 150 K and T = 300 K [24].

The impact of temperature on the drain current in a TFET depends on the region in which the TFET is operating [24]. Since different mechanisms of current transport are dominant in different regions of operation, the transfer characteristics exhibit different impacts of temperature in four regions of operation shown in Figure 5.9.

In Region-1, the TFET is in the OFF-state. In this region of operation, the drain current is independent of the gate voltage and is determined by the SRH generation-recombination current in the reverse-biased diode. Therefore, in Region-1 of operation, the drain current increases exponentially with temperature, since the SRH generation-recombination current is directly proportional to exp(−Eg/2kT) where Eg is the bandgap, T is the absolute temperature, and k is the Boltzmann constant [1, 24, 27, 50].

When the gate voltage is increased beyond the OFF-state, the TFET enters the subthreshold region of operation, which is shown as Region-2 in Figure 5.9. The average subthreshold swing in III-V TFETs normally increases as the temperature is increased and exhibits strong temperature dependence [9, 24, 27]. The primary reason for this behavior is the presence of the interface traps in the III-V TFETs. The tunneling of carriers from the valence band of the p+ source to the mid-gap trap levels followed by thermal emission of the carrier into the conduction band can explain the increase of the average subthreshold swing with temperature [9, 24].

When the gate voltage is increased further, the TFET enters Region-3 of operation. In this region of operation, the dependence of the drain current on temperature becomes weaker, since the drain current is primarily governed by BTBT [24, 50]. The weak temperature dependence is due to the dependence of the tunneling barrier on the bandgap Eg(T), which in turn is dependent on the temperature as follows [56]:



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