Blue quantum electroabsorption modulators based on reversed quantum confined Stark effect with blueshift

Abstract

The authors present the design, growth, fabrication, experimental characterization, and theoretical analysis of blue quantum electroabsorption modulators that incorporate ϳ5 nm thick In 0.35 Ga 0.65 N / GaN quantum structures for operation between 420 and 430 nm. Growing on polar c plane on sapphire, they obtain quantum structures with zigzag potential profile due to alternating polarization fields and demonstrate that their optical absorption blueshifts with applied electric field, unlike the redshift of conventional quantum confined Stark effect. In InGaN / GaN quantum structures, they report the largest absorption change of 6000 cm −1 for 6 V bias swing around 424 nm, holding promise for blue optical clock generation and injection directly into silicon chips. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2424642͔ Today silicon microelectronics is limited in operating speed: the electrical interconnects suffer from the RC limitation; scaling does not mitigate this problem.1 This leads to a bottleneck in electrical clocking. Optical clocking is proposed as a remedy.2 Optical clock distribution is implemented commonly in the near infrared ͑IR͒ spectral region where optoelecronic devices are readily available.3,4 However, silicon photodetectors, for example, those fabricated in standard complementary metal-oxide-semiconductor ͑CMOS͒ process, unfavorably exhibit long absorption length and thus a diffusion tail problem in the near IR. This limits the operating speed of Si CMOS photodetectors to 1 Gbits/ s. 5 To circumvent this problem, one approach is to utilize high-speed III-V photodetectors hybrid integrated on Si chips. This, however, introduces difficulties related to post-CMOS fabrication. On the other hand, unlike in the IR, optical clock injection directly to Si is possible in the blue, where Si features a very short absorption length ͑ϳ100 nm at 400 nm͒ and thus lacks the diffusion tail. 6 However, there exists no chip-scale device to modulate optical clock signal in the blue at high speeds to date. In this letter, we propose blue InGaN / GaN based quantum electroabsorption modulators for a possible chip-scale solution in optical clock modulation in the blue. Here we present the design, epitaxial growth, fabrication, experimental characterization, and theoretical analysis of our quantum electroabsorption modulators that incorporate ϳ5 nm thick In 0.35 Ga 0.65 N / GaN quantum structures in a p-i-n diode architecture for operation in the blue spectral range, as shown in Fig. 1.We grow these quantum structures on the polar c plane of GaN on sapphire in metal organic chemical vapor deposition ͑MOCVD͒ and obtain a zigzag potential profile due to high polarization fields with alternating directions in their heterostructures. We study the electroabsorption behavior of these quantum zigzag structures for proof-of-concept demonstration of their use in blue modulation. In the blue range, using InGaN / GaN quantum structures, we experimentally demonstrate the largest optical absorption change of 6000 cm −1 wi...

Violet to deep-ultraviolet InGaN∕GaN and GaN∕AlGaN quantum structures for UV electroabsorption modulators

“…This achieved electromodulation is the highest in InGaN / GaN based quantum structures compared to the previous reports. 5,22,23 ͑Also, here note that if only wells were taken as the thickness of the absorbing layer, these absorption coefficient changes would then be calculated to be even further larger with the respective values of 3.1ϫ 10 4 , 1.5ϫ 10 4 , and 1.3ϫ 10 4 cm −1 .͒ The absorption coefficient changes of these GaN / AlGaN based and InGaN / GaN based quantum electroabsorption modulators implies that an ϳ50 m long waveguide modulator with …”

“…1,2 In the visible spectral range, light emitting diodes, 3 laser diodes, 4 and electroabsorption modulators 5 have been demonstrated. Nowadays, a special interest of scientific research is also focused on the demonstration of ultraviolet ͑UV͒ optoelectronic devices.…”

Polar vs. nonpolar InGaN/GaN quantum heterostructures: Opposite quantum confined electroabsorption and carrier dynamics behavior

“…The absorption coefficient change (ǻĮ) in our InGaN/GaN quantum structures is significantly high, at a comparable level with other III-V quantum structures that operate at near infrared region and are widely used in telecom. This makes our devices promising candidates for their future use [5]. We also performed electroabsorption measurements in nonpolar structures.…”

“…In addition to this, the tilt in the quantum well layers' potential profile decreases and the energy difference between electron and hole ground states decreases. This effect can be probed through electroabsorption measurements and it is observed as a blueshift [5] in the absorption spectra at increasing external electric fields, i.e., reverse bias voltages, as in Figure 1. The absorption coefficient change (ǻĮ) in our InGaN/GaN quantum structures is significantly high, at a comparable level with other III-V quantum structures that operate at near infrared region and are widely used in telecom.…”

“…Moreover, in this semiconductor device platform, there is a great potential for even further expansion in optoelectronic device applications through innovation and development [4][5]. To widen their use, to improve their performances, and to expand their applications, physics of these devices should be understood well and materials quality and device efficiencies should be increased.…”