Prospective for graphene based thermal mid-infrared light emitting devices

Abstract

We have investigated the spatial and spectral characteristics of mid-infrared thermal emission from large area Chemical Vapor Deposition (CVD) graphene, transferred onto SiO2/Si, and show that the emission is broadly that of a grey-body emitter, with emissivity values of approximately 2% and 6% for mono- and multilayer graphene. For the currents used, which could be sustained for over one hundred hours, the emission peaked at a wavelength of around 4 μm and covered the characteristic absorption of many important gases. A measurable modulation of thermal emission was obtained even when the drive current was modulated at frequencies up to 100 kHz.

Boron nitride encapsulated graphene infrared emitters

“…Its low thermal mass (approximately three orders of magnitude smaller even than a typical silicon cantilever) offers the prospect for high frequency operation, and we have recently assessed the potential of using graphene based thermal emitters as an alternative, less complicated, approach to semiconductor LEDs. 14,15 For the currents used, the emission from these devices peaked at a wavelength of around 4 lm and a measureable modulation of the emission was observed up to a drive frequency of 100 kHz, much higher than in silicon based micro-heaters. However, these devices only operated in vacuum, and in this paper we demonstrate the use of hexagonal boron nitride (h-BN) as a means of encapsulating the emitting area, allowing sustained operation in air, and investigate how the incorporation of the h-BN layers modifies the thermal properties of the devices.…”

“…The emissivity of monolayer graphene has been previously measured as 1.6 6 0.8%, 11 in good agreement with the accepted value of the absorbance. In a multilayer device, the emissivity is expected to increase linearly with the number of layers, 14 as with the absorbance, 19 and in the devices studied here (which have 6-8 layers) the emissivity of the multilayer graphene is expected to be $10%. Heat loss through radiation is therefore also assumed to be smaller than that lost through diffusion and an approximate solution to Equation (1) is given then by 20…”

“…14 The line shown in Figure 2(c) was calculated using Equation (2) to obtain the temperature profile, and then by varying k to give the best fit to the measured data, yielding a characteristic length of 40 lm. This is two orders of magnitude larger than typical values, 0.1-0.2 lm, obtained from exfoliated graphene devices on SiO 2 substrates, 9 but reflects the effects of the multilayer graphene, the h-BN and the device geometry in these devices.…”

Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector

“…They found a wavelength-independent emissivity of (1.6 + 0.8) % in the near infrared, in agreement with measurements of optical absorption. Lawton et al 56 have investigated the spatial and spectral characteristics of midinfrared thermal emission from large area graphene deposited by CVD, transferred onto SiO 2 ∕Si, and found that the emission is broadly that of a gray-body emitter, with emissivity values of ∼2% and 6% for mono-and multilayer graphene. From Eq.…”

“…(13)] would be lowest for ε e ¼ 1 (perfect blackbody) and would be maximum for the lowest value of ε e . In this paper, to study the effect of emissivity on efficiency η of solar TEC, we consider ε e ¼ 1 (perfect blackbody) 54,53 for the values of η in Table 1 and ε e ¼ 0.016 (gray-body emitter) 55,56 for the values of η in Table 2. Comparing the first two rows (Table 1), we see that the efficiency increased from 45.6% to 50% when the emissivity ε s decreased from 1 to 0.08.…”