Double Negative Differential Resistance Device Based on Hafnium Disulfide/Pentacene Hybrid Structure

Abstract

Recently, combinations of 2D van der Waals (2D vdW) materials and organic materials have attracted attention because they facilitate the formation of various heterojunctions with excellent interface quality owing to the absence of dangling bonds on their surface. In this work, a double negative differential resistance (D-NDR) characteristic of a hybrid 2D vdW/organic tunneling device consisting of a hafnium disulfide/pentacene heterojunction and a 3D pentacene resistor is reported. This D-NDR phenomenon is achieved by precisely controlling an NDR peak voltage with the pentacene resistor and then integrating two distinct NDR devices in parallel. Then, the operation of a controllable-gain amplifier configured with the D-NDR device and an n-channel transistor is demonstrated using the Cadence Spectre simulation platform. The proposed D-NDR device technology based on a hybrid 2D vdW/organic heterostructure provides a scientific foundation for various circuit applications that require the NDR phenomenon.

Keywords: HfS2; hybrid structures; negative differential resistance (NDR); pentacene.

Figure 1

a) Schematic of the hybrid HfS₂/pentacene heterojunction, showing the interfaces of HfS₂/pentacene and pentacene/pentacene. b) Raman spectra of the HfS₂, pentacene, and overlapped HfS₂/pentacene regions. c) AFM image of a pentacene layer on SiO₂ and HfS₂. d) Core‐level X‐ray photoelectron spectra of the individual materials (HfS₂, pentacene) and heterojunctions (HfS₂/pentacene). Energy‐band alignments of HfS₂ and pentacene in the equilibrium state e) before and f) after the formation of the contact. The information on the energy bands was obtained from the previous XPS analysis.

Figure 2

a) Schematic of the NDR device based on the hybrid HfS₂/pentacene heterojunction. b) Optical image of the HfS₂/pentacene hybrid NDR device. c) I–V characteristic curve of the hybrid NDR device on a linear scale (left) and the corresponding differential resistance curve (right). d) Peak (blue square mark) and valley (red square mark) voltage values of four different hybrid NDR devices. e) Energy‐band diagrams of the hybrid NDR device in different operating‐voltage regions.

Figure 3

a) Cross‐sectional schematic of type‐1 and type‐2 NDR devices with different pentacene resistors and b) a corresponding optical image. c) Equivalent circuits, d) energy‐band diagrams, and e) I–V characteristic curves for the hybrid NDR devices. f) Calculated (black squares) and measured (red circles) peak voltages with respect to the pentacene resistance.

Figure 4

a) Schematic of the double‐peak hybrid NDR device consisting of two HfS₂/pentacene heterojunctions and one 3D pentacene resistor. b) Optical image of the double‐NDR device, where the equivalent circuits are indicated. c) I–V characteristic curve of the double‐NDR device. d) Circuit configuration of a controllable‐gain amplifier integrated with the double‐NDR device and an n‐channel transistor. e) Output AC signal (v _out, red/green/blue solid lines) corresponding to the input AC signal (v _IN, black solid line) under three different DC V _IN conditions (0.447/0.505/0.535 V). Summary table showing the input (v _IN = V _IN + v _in) and output (v _OUT = V _OUT + v _out) voltage conditions and the corresponding gain values. f) Load‐line analysis of the controllable‐gain amplifier circuit presenting amplified output AC signals at three different operating points (V _IN ± v _in: 0.447 ± 0.01, 0.505 ± 0.01, and 0.535 ± 0.01 V).