Electro-optic Coefficient Enhancement of Al_xGa_1–xN via Multiple Field Modulations

Abstract

AlGaN has attracted growing interest for applications in electro-optic devices that generate and process optical signals. To enhance the electric-optic effect with polarity, we designed and grew GaN/AlxGa1-xN quantum structures with x of about 0.5 by metal-organic vapor-phase epitaxy. Spectroscopic ellipsometry measurement and ab initio calculation demonstrated that the stronger polarization fields induced by higher Al contents in the barrier result in larger electro-optic effects. By applying external biases directly on both sides of these quantum structures, a high intensity of external field was achieved, and extraordinary and ordinary refractive indices were characterized by fitting the variable-angle spectroscopic ellipsometry. The values of deduced electric-optic coefficients were significantly enhanced by combining the resonance effect with the internal and external fields. Given the comparable electric-optic coefficients with conventional electro-optic crystals, AlGaN is an attractive candidate for nonlinear optical material, which provides a basis for large-scale integrations of ultraviolet electro-optic devices based on nitride semiconductors.

Enhanced Pockels Effect in AlN Microring Resonator Modulators Based on AlGaN/AlN Multiple Quantum Wells

“…The huge internal polarization field can induce the third-order nonlinear effect and increase the effective nonlinearity in the AlGaN/AlN MQW layer. 36,37,39,40 Similar enhancement is found for MRMs on sample B. All parameter values for extracting χ eff (2) of samples A and B and bare AlN are listed in Table 2.…”

“…Thus, in this study, we investigate MQW layers with optimized structures that provide a high internal Figure 1. Reported Pockels coefficient (r 13 and r 33 ) and their cutoff wavelengths for different materials: LiNbO 3 , 26−34 GaN, 35 GaN/ AlGaN MQWs, 36,37 AlN, 23−25 and AlGaN/AlN MQWs (our study). The error bar shows the spectral dependence of the EO coefficient.…”

“…39,40 A more recent work utilized a high internal polarization field based on GaN/ AlGaN superlattices to produce a 10 times higher Pockels coefficient than bare GaN, shown in Figure 1 additional freedom for manipulating the EO effect. 36,37 The error bar in Figure 1 shows the variation of the Pockels coefficient within the wavelength (see Section S1 in the Supporting Information for details). The Pockels coefficient of GaN/AlGaN multiple quantum wells (MQWs) from ref 36 is competitive with LiNbO 3 and offers even higher values near the band edge due to the resonance effect.…”

Integral Monolayer-Scale Featured Digital-Alloyed AlN/GaN Superlattices Using Hierarchical Growth Units

“…Aluminum gallium nitride (AlGaN), an essential compound semiconductor for III-nitrides material systems, has attracted considerable attention in recent years. These systems hold various promising applications in many fields, such as ultraviolet/deep ultraviolet optoelectronic devices, confidential optical communication in space, and chemical/biological agent sensing, thanks to their wide direct band-gaps with great adjustability and great physical, chemical, and mechanical stability. − Many efforts have been put into obtaining AlGaN films with high Al content. However, it still remains challenging to prepare epitaxial AlGaN with atomically sharp interfaces, and negligible compositional fluctuations, due to the large lattice mismatch and strong vapor-phase prereaction during growth. − Some researchers reported eliminating vapor-phase prereaction during the epitaxy of AlGaN films with high Al content by optimizing the V/III ratio and reactor pressure .…”

Electric field mapping of wide-bandgap semiconductor devices at a submicrometre resolution

“…The electric field is mainly present in and very near to the device channel and hence this is where the measured EFISHG signal originates. The third-order nonlinear susceptibility of the AlGaN/GaN interface 27,28 was reported to be two orders of magnitude larger than that of GaN 29 and SiC 30 , and three orders of magnitude larger than Si 3 N 4 31 . This means the EFISHG signal from the channel region dominates over the signal from Si 3 N 4 passivation, GaN buffer and SiC substrate layers; electric field determined then reflects channel in-plane electric field averaged over the lateral spatial resolution.…”