Controllable fabrication and characterization of suspended graphene/hexagonal boron nitride heterostrcuture Joule heating infrared radiation devices (invited)

  Objective  Graphene exhibits superior optical, electrical, thermal, and mechanical properties, while the suspended structure avoids external factors such as wrinkles, carrier scattering and doping caused by rough substrates, and can maximize the intrinsic physical properties of graphene, which is of great significance in the research of high-performance graphene microelectronics and optoelectronic devices. However, the current research on suspended graphene devices is yet limited by the complicated fabrication methods, low yield, and unstable electrical and thermal properties of devices.

  Methods  In order to improve the yield rate of suspended graphene nano devices and the comprehensive performance of the device, this paper develops a method by using two-dimensional material hexagonal boron nitride (h-BN) to pick up graphene, then transfers graphene directly to the surface of pre-fabricated metal electrodes, and finally prepares suspended graphene Joule heating infrared radiation devices (Fig.1). In order to further reduce the defects and improve the device quality, a high-vacuum thermal annealing treatment was performed on the suspended graphene device. Based on the high-quality suspended graphene device after annealing, we used Raman spectroscopy and luminescence spectroscopy to study the temperature characteristics and thermal radiation spectral characteristics of the device under the Joule heating effect caused by bias voltage.

  Result and discussion   The experimental results show that the h-BN covers the upper surface of the graphene and plays a critical role in supporting and suspending the graphene, which effectively improves the stability of the suspended graphene and avoids device failures such as collapse and fracture. After the thermal annealing at 400 ℃/3 h in high vacuum of 4.5×10⁻⁴ hPa, the resistance of suspended graphene decreased to one-sixth of that before annealing, and the carrier mobility increased eighteen times compared with that before annealing (Fig.4). When the bias voltage is 8 V, the temperature of suspended graphene measured by Raman spectroscopy is 836 K, and it shows a strong infrared radiation signal at 955 nm wavelength (Fig.5).

  Conclusions  This paper presents a controllable fabrication method of high-quality suspended graphene Joule heating radiation devices, and investigates the electrical, temperature, and thermal radiation characteristics of suspended graphene devices. The h-BN in the device structure demonstrates a good support and adhesion effect for suspended graphene, which greatly improves the device performance. The impurities attached to the surface of graphene can be effectively removed through high vacuum thermal annealing, which greatly improves the electrical performance of suspended graphene devices. It was observed that the temperature of graphene increased with the increase of bias voltage, showing a blue shift in the Raman spectrum and strong thermal radiation emission. The research results of this paper provide an important reference for deepening the understanding of the intrinsic physical properties of suspended graphene and developing optoelectronic applications based on suspended graphene devices.