GeSn-on-Si normal incidence photodetectors with bandwidths more than 40 GHz

Abstract

GeSn (Sn content up to 4.2%) photodiodes with vertical pin structures were grown on thin Ge virtual substrates on Si by a low temperature (160 °C) molecular beam epitaxy. Vertical detectors were fabricated by a double mesa process with mesa radii between 5 µm and 80 µm. The nominal intrinsic absorber contains carrier densities from below 1 · 10(16) cm(-3) to 1 · 10(17) cm(-3) for Ge reference detectors and GeSn detectors with 4.2% Sn, respectively. The photodetectors were investigated with electrical and optoelectrical methods from direct current up to high frequencies (40 GHz). For a laser wavelength of 1550 nm an increasing of the optical responsivities (84 mA/W -218 mA/W) for vertical incidence detectors with thin (300 nm) absorbers as function of the Sn content were found. Most important from an application perspective all detectors had bandwidth above 40 GHz at enough reverse voltage which increased from zero to -5 V within the given Sn range. Increasing carrier densities (up to 1 · 10(17) cm(-3)) with Sn contents caused the depletion of the nominal intrinsic absorber at increasing reverse voltages.

Dislocation density and strain-relaxation in Ge 1−x Sn x layers grown on Ge/Si (0 0 1) by low-temperature molecular beam epitaxy

“…The spectral response of Ge1-xSnx based photodetectors now extends all the way up to 2.4 m [11]. Progress made recently, towards improvement of material quality and fabrication technology, has also led to realization of high speed p-i-n photodetectors, operating at a bandwidth of up to 40 GHz [12].…”

Optical Characterization of Si-Based Ge1−x Sn x Alloys with Sn Compositions up to 12%

“…1 Among the various material systems that could be integrated on Si, the Ge 1Àx Sn x alloy has attracted much attention recently due to the following reasons: (1) Capability of monolithic integration on Si; 2 (2) Availability of direct bandgap material; 3 and (3) tunable bandgap covering broad shortwave-and mid-infrared (IR) wavelength range. 4 During the last decade, the GeSn-based optically pumped laser, 5 light emitting diode, [6][7][8][9][10][11][12] photo detector [13][14][15][16][17][18][19][20] have been demonstrated, and the GeSn modulator has been investigated 21,22 which make up a complete set of components for Si photonics. For these prototype devices, the material characteristics have turned out to be the decisive factor for the performance of the device.…”

Germanium-Tin on Si Avalanche Photodiode: Device Design and Technology Demonstration

“…The absorption range of Ge 1−x Sn x can be substantially extended to infrared by increasing its tin composition [36], making it a very promising absorbing material in NIR photodetectors. Ge 1−x Sn x NIR photodetectors based on both metal-semiconductor-metal [37]- [39] and p-i-n [40]- [45] structures have been reported.…”