Quantum modeling of electron confinement in double triangular quantum well formed in nanoscale symmetric double-gate InAlAs/InGaAs/InP HEMT

Abstract

The electron confinement in double triangular quantum wells (DTQW) in nanoscale symmetric Double gate InAlAs/InGaAs/InP HEMT (DGHEMT) has been modeled and simulated including quantum effects at gate lengths (L g ) 100nm and 50nm. The trend towards thinner channel and shorter gate lengths is resulting in increased importance of quantum effects, as many of the semi-classical assumptions become invalid. At nanoscale-dimensions, there is a need to imagine the carriers as particle-waves rather than semi-classical particle and it becomes imperative to study the electron confinement in the channel quantum mechanically instead of semi-classically. The standard approach being followed earlier has been within semi-classical framework for a double gate InAlAs/InGaAs/InP HEMT. Most of the quantum simulations have been performed for single gate HEMT [1]. DGHEMT are very promising for high frequency [2] and low noise applications and hence quantum modeling of this device is required. This paper introduces a quantum model to investigate the DTQW consisting of two single triangular quantum wells formed in semiconductor InGaAs sandwiched between layers of InAlAs material with a wider bandgap. The quantum model used to simulate the channel confinement is Quantum Moments (Density Gradient) Model which accurately reproduces the carrier concentration in the channel. In order to facilitate our study at 50nm, the vertical dimensions are not scaled down when reducing L g from 100nm to 50nm. Simulated structure of symmetric DGHEMT is shown in Fig.1, device dimensions are given in Table. I and electron concentration profiles in DTQW at (L g ) 100nm and 50nm are shown in Fig. 2 and Fig. 3 Comparison with the semi-classical model predicts that at nanodimensions, the effects of quantum confinement become so pronounced that the double triangular quantum well formed in the channel seems to behave as a single quantum well and shows the peak electron concentration at the centre of the channel. To conclude, the quantization of electron confinement in DTQW in nanoscale DGHEMT has been modeled by a quantum moments model and it can be seen that the peak electron concentration exists at the two channel interfaces with the spacer layers in semi-classical representation while quantum model shows the maximum electron concentration in the centre of the channel indicating double triangular quantum wells behaving as a single quantum well. Also Drain characteristics (I d -V ds ) comparing semi-classical and quantum models with experimental results [3] have been shown in Fig. 4 for L g =100nm, keeping V gs constant at −0.1V and plotting I d as a function of V ds respectively. The proposed quantum model shows a good matching with the experimental results [3] in the linear region with only a slight reduction in the saturation current is observed in the quantum model. For DGHEMT having their gate lengths in the nanometric scale, our simulation emphasizes on the importance of quantum modeling of the channel so as to have a proper representation of the nanodimension device.