Monolithic Ge-on-Si lasers for large-scale electronic–photonic integration

Abstract

A silicon-based monolithic laser source has long been envisioned as a key enabling component for large-scale electronic-photonic integration in future generations of high-performance computation and communication systems. In this paper we present a comprehensive review on the development of monolithic Ge-on-Si lasers for this application. Starting with a historical review of light emission from the direct gap transition of Ge dating back to the 1960s, we focus on the rapid progress in band-engineered Ge-on-Si lasers in the past five years after a nearly 30-year gap in this research field. Ge has become an interesting candidate for active devices in Si photonics in the past decade due to its pseudo-direct gap behavior and compatibility with Si complementary metal oxide semiconductor (CMOS) processing. In 2007, we proposed combing tensile strain with n-type doping to compensate the energy difference between the direct and indirect band gap of Ge, thereby achieving net optical gain for CMOS-compatible diode lasers. Here we systematically present theoretical modeling, material growth methods, spontaneous emission, optical gain, and lasing under optical and electrical pumping from band-engineered Ge-on-Si, culminated by recently demonstrated electrically pumped Ge-on-Si lasers with >1 mW output in the communication wavelength window of 1500-1700 nm. The broad gain spectrum enables on-chip wavelength division multiplexing. A unique feature of band-engineered pseudo-direct gap Ge light emitters is that the emission intensity increases with temperature, exactly opposite to conventional direct gap semiconductor light-emitting devices. This extraordinary thermal anti-quenching behavior greatly facilitates monolithic integration on Si microchips where temperatures can reach up to 80 • C during operation. The same band-engineering approach can be extended to other pseudo-direct gap semiconductors, allowing us to achieve efficient light emission at wavelengths previously considered inaccessible.

Ge-on-Si photonic devices for photonic-electronic integration on a Si platform

“…Furthermore, such an n-type tensile-strained Ge revealed an optical gain [53]. In a Fabry-Perot resonator of Ge waveguide, a lasing was also reported under an optical pumping [54] and an electrical pumping [55,56], although there is no further report to obtain the lasing. In order to generate a large (> 1%) tensile strain towards direct-gap Ge, an application of micromechanical stress [57] to membrane structures [58,59,60,61] was examined, but no lasing has been obtained yet.…”

Direct bandgap type-I GeSn/GeSn quantum well on a GeSn- and Ge- buffered Si substrate

“…[1][2][3][4][5][6][7][8][9] The successful demonstration of direct bandgap GeSn light emitting diodes (LEDs), and optically-pumped GeSn lasers, [10][11][12][13][14] indicates the great potential of GeSn for Si-based light sources. GeSn LEDs with double heterostructures (DHS) 11,[15][16][17][18][19][20][21][22] and quantum wells (QWs) [23][24][25][26][27][28][29][30][31] have been reported.…”

Silicon photonics devices for integrated analog signal processing and sampling

“…Optical gain has been achieved in a silicon system by the incorporation of other materials. For electrically pumped sources, methods include hybrid integration of III-V [53] and germanium lasers [54]. III-V integration requires non-standard and challenging fabrication steps, negating many of the benefits of silicon photonics technology over an all III-V photonics technology.…”