## 3 Results and Discussion  
To analyze the h-BN layer itself, the produced h-BN on polycrystalline Cu foil was transferred to a Si substrate. The scanning electron microscopy (SEM) images of the h-BN layer after it was relocated to a Si substrate is shown in Figure 2a,b. These indicate that the h-BN layer has a tearing-free two-dimensional nanosheet structure. However, there are a few wrinkles on the surface. The discrepancy in thermal expansion coefficients between Cu foil and h-BN was blamed [16]. A transmission electron microscopy image of the atomic arrangement of the h-BN sheet is shown in Figure 2c. The organization of B and N atoms in a single hexagonal lattice was clearly observed [17]. Furthermore, because Raman spectroscopy has become an important method for characterizing and investigating two-dimensional materials, we used it to further study the h-BN monolayer crystal structure. Figure 2d shows the Raman spectra of transferred h-BN on a Si substrate; it showed a G band centered at 1370 cm\({}^{-1}\), which corresponds to the E\({}_{\text{2g}}\) vibration mode in h-BN. It was reported that the G band frequency of bulk h-BN was observed to be at 1366.6 \(\pm\) 0.2 cm\({}^{-1}\), which upshifted to 1369.6 \(\pm\) 0.6 cm\({}^{-1}\) when the substrate was atomically monolayer h-BN. This makes sense when the stronger E\({}_{\text{2g}}\) phonons are considered, which result in a blueshift in the G band. In addition, the full width at half maximum was only 21.7 cm\({}^{-1}\). These signatures indicating high crystalline quality of h-BN monolayers can be verified using both TEM and Raman techniques [18,19]. Figure 3a,b show the current-voltage (I-V) characteristics of manufactured LEDs with and without an h-BN passivation layer at forward and reverse bias, respectively. The forward voltages for both devices are 3.8 V at a 20 mA injection current. Because the h-BN layer has no influence on the device, contact resistance, or stress, the results are the same for both devices in forward bias. Figure 3b shows that the leakage current drops by about one order from 1.09 \(\times\) 10\({}^{-8}\) to 1.15 \(\times\) 10\({}^{-9}\) A at \(-\)5 V, when the bias is reversed. This finding suggests that the monolayer h-BN is effective in LED passivation, lowering the reverse leakage current through the LED's surface. The leakage current is minimized because the h-BN successfully passivates the defects on the device's surface and mesa sidewall [20]. The EL at 20 mA and light output power of both devices are shown in Figure 3c,d, respectively. Both measurement results show that after h-BN passivation, light output performance is somewhat improved. In the visible range of 460 nm, which is the wavelength of the fabricated LEDs, monolayer h-BN has a transmittance of more than 90%, which means that the majority of the light is transmitted. The device's leakage current was lowered after h-BN application due to a passivation effect, and the intensity of EL was improved. In  
Figure 1: Schematic diagram of fabricated InGaN/GaN-based light-emitting diode (LED) with hexagonal boron nitride (h-BN) film as a passivation layer. comparison to the traditional LED, the EL peak of the LED with h-BN exhibits a minor blue shift. The blue shift in the LED with h-BN passivation can be attributed to a reduced band gap shrinking due to efficient heat dispersion via h-BN [21]. Figure 4a,b are infrared camera images during the operation of reference LEDs and LEDs with h-BN passivation, respectively. As seen in the images, heat surrounding the contact is not concentrated, as shown by an infrared camera image of a 350 \(\upmu\)m \(\times\) 350 \(\upmu\)m area LED with h-BN passivation. Most of the heat is generated by current crowding in the p-type contact, which causes the temperature of the device to rise [22].