Principal Investigator Jesus del Alamo
InGaAs is a promising n-channel material candidate for future CMOS technology due to its superior electron transport properties and low voltage operation. Due to the lack of good native oxide, it has been challenging to achieve a high-quality gate stack, which includes the gate oxide as well as the oxide/semiconductor interface. Many have observed hysteresis and threshold voltage instability in InGaAs MOSFETs that are attributed to interface and oxide defects. In this work, we study the frequency dispersion of InGaAs MOSFETs, an import- ant electrical parameter that is also affected by gate stack defects.
The InGaAs MOSFETs used in this study are fabricated in a contact-first, gate-last self-aligned manner. The intrinsic channel consists of 8 nm-thick In0.7Ga0.3As. The gate insulator is a 2.5 nm-thick HfO2, deposited by Atomic Layer Deposition (ALD) at 250oC. The gate metal Mo is 35 nm thick, deposited by evaporation.
These devices show state-of-the-art performance. We have carried out frequency-dependent electrical characterization from DC to 10 GHz. For the frequency range between 100 kHz and 10 MHz, we employ a lock- in setup and measure the AC drain current induced by (a) AC gate voltage. For frequency range from 100 MHz to 10 GHz, the device S-parameters are measured using a vector network analyzer. From these measurements, we extract the intrinsic transconductance, gm,i. The frequency shows the dispersion of the intrinsic transconductance (gm,i) from DC to 10 GHz. As AC frequency increases, deep-level trap states can no longer respond, and device performance improves. gm,i increases from 775 mS/mm to 2200 mS/mm from DC to 10 GHz. The dispersion throughout the entire frequency range also indicates defect states with different time constants. It is remarkable how much unrealized intrinsic performance is left at DC. We show peak gm,i at 10 GHz as a function of gate voltage. Here it is clear that the higher the gate voltage, the larger the gap between DC and 10 GHz gm,i. At the highest gm,i, the ratio is about a factor of 3.
In conclusion, we have found large frequency dispersion of intrinsic transconductance in InGaAs MOSFETs, leading to a compromised device performance at DC. Thus, it is important to mitigate the oxide and interface defects in order to unveil the intrinsic outstanding transport properties of InGaAs.