$N$- and $P$-type symmetric scaling behavior of monolayer hydrogenated boron arsenide transistors

High thermal conductivity and ambipolar mobility are highly desirable for semiconductors in electronics and have been observed in bulk boron arsenide (BAs). In this work, we explore the scaling behavior of a monolayer hydrogenated BAs field-effect transistor (ML H-BAs FET) by employing ab initio quantum transport methods. Both the armchair- and zigzag-directed ML H-BAs FETs can well satisfy the requirements of the International Technology Roadmap for Semiconductors even if the gate length is scaled down to $2\sim 3$ nm for high-performance applications. The excellent n- and $p\text{−}\mathrm{type}$ symmetry of bulk BAs is well preserved in the ML H-BAs FET along with the zigzag direction but is lost in the armchair direction. However, such asymmetry can be suppressed by applying uniaxial compressive strain owing to the broken valence band degeneracy. Our findings provide important theoretical insights into transport symmetry and the scaling behavior of ML H-BAs FETs.

Figure 1

(a) Top and side views of the ML H-BAs. (b) The electronic band structures and density of states (DOS) of the monolayer H-BAs. (c) The eigenstates for the conduction band minimum (CBM) and valence band maximum (VBM) of the ML H-BAs. (d) The schematic view of the DG ML H-BAs with the underlap (UL) structure.

Figure 2

$I–V_{\mathrm{g}}$ characteristics of the $n-$ and $p\text{−}\mathrm{type}$ ML H-BAs MOSFETs along with the (a), (b) armchair and (c), (d) zigzag directions.

Figure 3

Gate length $L_{\mathrm{g}}$ scaling of the (a) on-state current $I_{\mathrm{on}}$, (c) transconductance $g_{\mathrm{m}}$, (e) subthreshold swing $\mathit{SS}$, (d) total gate capacitance $C_{\mathrm{t}}$, (e) delay time τ, (f) power dissipation PDP for the $n-$ and $p\text{−}\mathrm{type}$ ML H-BAs MOSFETs along with the armchair and zigzag directions.

Figure 4

(a) PDP versus τ of the $n-$ and $p\text{−}\mathrm{type}$ ML H-BAs MOSFETs along with the armchair and zigzag directions. The dashed lines represent $\mathrm{PDP}=\frac{\mathrm{EDP}}{\tau }$, where the EDP is the abbreviation of the energy-delay product. The ratio of (b) $I_{\mathrm{on}}$ and (c) $\mathit{SS}$ between the NMOS and PMOS with the same channel material, including the ML H-BAs, H-GaAs, H-InP, and silicane [23, 46, 47].

Figure 5

(a)–(f) Energy band structure of ML H-BAs with and without the uniaxial compressive strain $\alpha =-2\sim -12\%$ along with the armchair direction. The indirect/direct bandgap properties are the result of energy competition among the near-band-edge states A–C. Dashed lines indicate the energy shifts of CBM and VBM.

Figure 6

(a)–(c) Bloch state energy contour diagram of near-band-edge states A–C of ML H-BAs under uniaxial strain $\alpha =-4\%$. States A and B are bonding along with the armchair direction while state C is antibonding. (d) The energy of near-band-edge states A-C as a function of applied uniaxial strain.

Figure 7

(a) Band gap and hole effective mass under the uniaxial strain α for the ML H-BAs. (b) The $p_{\mathrm{x},\mathrm{y}}$ orbitals of the ML-H-BAs valence band without and with strain (upper panel). The schematics of ML H-BAs under uniaxial compressive strain (lower panel). (c) The projected band structures of ML H-BAs onto the $p_{\mathrm{x}}$ and $p_{\mathrm{y}}$ orbitals. (d) The energy contour plots of the highest valence band of ML H-BAs without and with strain.

Figure 8

(a) UL-optimized $I_{\mathrm{on}}$ for the $p\text{−}\mathrm{type}$ ML H-BAs MOSFET along with the armchair direction under the uniaxial strain α. (b) The N/PMOS ratio of $I_{\mathrm{on}}$ without and with uniaxial strain. (a) Local device density of states and spectral currents of the $p\text{−}\mathrm{type}$ ML H-BAs MOSFETs along with the armchair direction (c) without and (d) with uniaxial strain. Corresponding $L_{\mathrm{g}}$ and $L_{\mathrm{UL}}$ are 1 and 4 nm, respectively. $V_{\mathrm{dd}}=\left({\mu }_{\mathrm{s}}–{\mu }_{\mathrm{d}}\right)/e=0.55$ V.