Genquan Han

Design of GeSn-Based Heterojunction-Enhanced N-Channel Tunneling FET With Improved Subthreshold Swing and ON-State Current

We design a heterojunction-enhanced n-channel tunneling FET (HE-NTFET) employing a Ge_1-xSn_x/Ge_1-ySn_y (x > y) heterojunction located in the channel region with a distance of L_T-H from the source-channel tunneling junction. We investigate the impact of L_T-H on the performance of HE-NTFETs by simulation. HE-NTFETs achieve a positive shift of VONSET, a steeper subthreshold swing (SS), and an enhanced ION compared with homo-NTFETs, which is attributed to the modulating effect of heterojunction on band-to-band tunneling (BTBT). At a supply voltage of 0.3 V, 304% ION enhancement is demonstrated in the Ge_0.92Sn_0.08/Ge_0.94Sn_0.06 HE-NTFET with a 4 nm L_T-H over Ge0.92Sn0.08 homo-NTFET due to the steeper average SS. The impact of Sn composition on the performance of HE-NTFETs is also studied. As we increase the difference in Sn composition x - y across the heterojunction, ION and SS of HE-NTFETs are improved due to the increase in band offsets at the Ge_1-xSn_x/Ge_1-ySn_y interface, which leads to the enhanced modulating effect of heterojunction on BTBT.

Strained GeSn p-Channel Metal–Oxide–Semiconductor Field-Effect Transistors With In Situ Si 2 H 6 Surface Passivation: Impact of Sn Composition

We report a study about the impact of Sn composition on the performance of strained germanium-tin (GeSn) pMOSFETs. GeSn pMOSFETs with Sn compositions of 0.027, 0.040, and 0.075 were fabricated on Ge(001) with an in situ Si₂H₆ passivation. Enhancement in drive current and transconductance is obtained for GeSn pMOSFETs with higher Sn composition due to the smaller capacitance equivalent thickness, the reduced source/drain resistance, and the improved effective hole mobility μeff. Right shift of threshold voltage with Sn composition is observed for the devices. Ge_0.973Sn_0.027, Ge_0.960Sn_0.040, and Ge_0.925Sn_0.075 pMOSFETs demonstrate the peak μ_eff of 340, 378, and 496 cm²/Vs, respectively. At an inversion charge density of 5 × 10¹² cm^-2, Ge_0.925Sn_0.075 pMOSFETs demonstrate 36% and 24% enhancement in μ_eff compared with Ge_0.973Sn_0.027 and Ge_0.960Sn_0.040 devices, respectively. Simulation shows that the enhancement in μeff with Sn composition is resulted from the reduction of hole effective mass and intervalley scattering between heavy and light holes caused by the increased compressive strain.

Theoretical investigation of tensile strained GeSn waveguide with Si 3 N 4 liner stressor for mid-infrared detector and modulator applications

We theoretically investigate a tensile strained GeSn waveguide integrated with Si₃N₄ liner stressor for the applications in mid-infrared (MIR) detector and modulator. A substantial tensile strain is induced in a 1 × 1 μm² GeSn waveguide by the expansion of 500 nm Si₃N₄ liner stressor and the contour plots of strain are simulated by the finite element simulation. Under the tensile strain, the direct bandgap E(G,Γ) of GeSn is significantly reduced by lowering the Γ conduction valley in energy and lifting of degeneracy of valence bands. Absorption coefficients of tensile strained GeSn waveguides with different Sn compositions are calculated. As the Si₃N₄ liner stressor expands by 1%, the cut-off wavelengths of tensile strained Ge(0.97)Sn(0.03), Ge(0.95)Sn(0.05), and Ge(0.90)Sn(0.10) waveguide photodetectors are extended to 2.32, 2.69, and 4.06 μm, respectively. Tensile strained Ge(0.90)Sn(0.10) waveguide electro-absorption modulator based on Franz-Keldysh (FK) effect is demonstrated in theory. External electric field dependence of cut-off wavelength and propagation loss of tensile strained Ge(0.90)Sn(0.10) waveguide is observed, due to the FK effect.

Germanium-Tin P-channel tunneling field-effect transistors: Impacts of biaxial tensile strain and surface orientation

This work investigates the impacts of biaxial tensile strain and surface orientation on performance of GeSn pTFET. Multi-bands k·p method is used to calculate the band structure of biaxially tensile strained GeSn on various orientations. The electrical characteristics of tensile strained GeSn line- and point-pTFETs are computed implementing the dynamic nonlocal BTBT algorithm. Our simulation demonstrates that 1) tensile strained GeSn pTFETs achieve significantly improved |ION| over relaxed devices; 2) With the same tensile strain, GeSn pTFETs on (011) and (111) orientations demonstrate higher |ION| compared to (001)-oriented device.

Simulation investigation of tensile strained GeSn fin photodetector with Si 3 N 4 liner stressor for extension of absorption wavelength

In this paper, we design a biaxial tensile strained GeSn photodetector with fin structure wrapped in Si(3)N(4) liner stressor. A large biaxial tensile strain is induced in GeSn fins by the expansion of Si(3)N(4) liner stressor. The distribution of tensile strain in GeSn fins was calculated by a finite element simulation. It is observed that magnitude of the strain increases with the reduction of fin thickness T(fin). Under the biaxial tensile strain, the direct band gap E(G,Γ) of GeSn fin photodetector is significantly reduced by lowering Γ conduction valley in energy and lifting of degeneracy of valence bands. As the 30 nm Si(3)N(4) liner stressor expanses by 1%, a E(G,Γ) reduction of ~0.14 eV is achieved in Ge(0.92)Sn(0.08) fins with a T(fin) of 100 nm. The cut-off wavelengths of strained Ge(0.96)Sn(0.04), Ge(0.92)Sn(0.08) and Ge(0.90)Sn(0.10) fin photodetectors with a T(fin) of 100 nm are extended to 2.4, 3.3, and 4 μm, respectively. GeSn fin photodetector integrated with Si(3)N(4) liner stressor provides an effective technique for extending the absorption edge of GeSn with Sn composition less than 10% to mid-infrared wavelength.

The Transmission Characteristic of Metal–Dielectric–Metal Slot Waveguide-Based Nanodisk Cavity With Gain Medium

We theoretically investigate the propagation of surface plasmon polaritons (SPPs) for the metal-dielectric-metal slot waveguide coupled to a disk cavity filled with gain material. The transmission and reflection characteristics of the resonant structure are numerically analyzed based on coupled-mode theory. The influence of structure parameters on the spectra of transmission is investigated using a finite-element method. In addition, the incorporation of gain medium can compensate for the loss from metal and, thus, enable the loss-negligible SPP propagation in near-infrared wavelengths, which makes a novel approach of optical switches and lasers based on SPPs possible in the planar optoelectronic compact integration.

Tensile-Strained Mid-Infrared GeSn Detectors Wrapped in Si 3 N 4 Liner Stressor: Theoretical Investigation of Impact of Device Architectures

In this paper, we comparatively studied the energy band diagram and the cutoff wavelength characteristics of germanium-tin (GeSn) fin and pillar array detectors wrapped in a Si₃N₄ liner stressor to unveil the impacts of tensile strain and device architecture in the absorption spectra of the devices. A large tensile strain is introduced into GeSn devices by the expansion of the Si₃N₄ liner stressor. Compared to the fin detector, a larger tensile volume strain is demonstrated in the GeSn pillar architecture. With the tensile strain induced by the Si₃N₄ liner stressor, the direct bandgap E_G,Γ of GeSn is obviously shrinked by lowering the energy of the Γ conduction band valley, which results in a significant extension of absorption edge in the GeSn detectors. As the Si₃N₄ liner stressor releases internal stress and expands, the absorption edge of the tensile-strained Ge_0.90Sn_0.10 pillar array detector with the length of side of pillar L_pillar of 100 nm is extended to 4.35 μm. With further improvement, the tensile-strained GeSn pillar architecture with the Si₃N₄ liner stressor will be competitive for the application in 2-5-μm mid-infrared spectra.

Temperature dependent IDS–VGS characteristics of an N-channel Si tunneling field-effect transistor with a germanium source on Si(110) substrate

We fabricated n-type Si-based TFETs with a Ge source on Si(110) substrate. The temperature dependent IDS–VGS characteristics of a TFET formed on Si(110) are investigated in the temperature range of 210 to 300 K. A study of the temperature dependence of ILeakage indicates that ILeakage is mainly dominated by the Shockley-Read-Hall (SRH) generation—recombination current of the n+ drain—Si substrate junction. ION increases monotonically with temperature, which is attributed to a reduction of the bandgap at the tunneling junction and an enhancement of band-to-band tunneling rate. The subthreshold swing S for trap assisted tunneling (TAT) current and band-to-band tunneling (BTBT) current shows the different temperature dependence. The subthreshold swing S for the TAT current degrades with temperature, while the S for BTBT current is temperature independent.

Gain-assisted propagation of surface plasmons in nanodisk resonator

Gain medium is introduced into the nanodisk resonator to enable loss-negligible surface plasmon polaritons propagation in near-infrared wavelengths, which benefits the applications of switches and lasers based on SPPs in the planar optoelectronic densely integration.

Tensile strained Ge0.90Sn0.10 photodiode integrated with Si3N4 liner stressor for mid-infrared applications

In this paper, tensile strained Ge0.90Sn0.10 photodiode with different architectures integrated with Si3N4 liner stressor for mid-infrared applications are theoretically investigated. Ge0.90Sn0.10 fin and waveguide photodiodes wrapped in the Si3N4 liner stressor are designed and the strain distribution is studied by the finite element simulation. A large tensile strain is induced in Ge0.90Sn0.10 with the Si3N4 liner stressor expanding. The energy band structure of tensile strained Ge0.90Sn0.10 is calculated using k⋅p theory. The direct bandgap Eg,Γ of Ge0.90Sn0.10 under tensile strain is significantly reduced, which results in a large red shift of the cut-off wavelength of strained Ge0.90Sn0.10 devices. As the Si3N4 liner stressor expands by 1.5%, 25.1% and 48.7% reduction of Eg,Γ are achieved in tensile strained Ge0.90Sn0.10 fin and waveguide photodiodes, respectively, compared to the unstrained device. The cut-off wavelengths of tensile strained Ge0.90Sn0.10 fin and waveguide devices are extended to 3.68 μm and 5.37 μm, respectively. Introducing tensile strain into GeSn by tensile strain liner stressor provides an effective method for extending the detection spectrum of GeSn photodiodes to mid-infrared wavelength, e.g. 5μm.