Vertical germanium nanowires as spectrally-selective absorbers across the visible-to-infrared

Abstract

Nanostructuring a material permits control over its interaction with light. Advanced methods for controlling the visible-to-infrared absorption spectra of semiconductor materials would present opportunities for photodetectors with engineered spectral response. Here, we experimentally demonstrate the fabrication of arrays of vertical Ge nanowires with different diameters. Measured reflection spectra show dip features for which electromagnetic simulations predict enhanced absorption. These can be shifted to longer wavelengths by increasing the diameters of the nanowires. We show that the reflectance dips broaden if the nanowires exhibit tapering. We furthermore show that observed ripple features in the dips are associated with longitudinal modes of the nanowires.

Germanium Nanowires as Spectrally-selective Photodetectors in the Visible-to-Infrared

“…2a predict peaks in absorption spectra, whose position shifts to longer wavelength with increasing NW diameter. The peaks in absorption correspond to reflection dips in our previous study [5], and are due to wavelength dependent resonant light absorption in guided modes of the NW. The spectral responses of the fabricated devices were found from measurements with a homemade set-up.…”

“…Furthermore, for multispectral imaging at SWIR wavelengths, the current approach [4] involves mounting broadband image sensors on bulky spectrometers. In our recent work [5], we suggested the use of germanium NWs as photodetectors due to their potential for low cost, SWIR sensitivity and ease of nanostructuring as a CMOS compatible material. A novel approach was proposed by using Ge NWs nanofabricated on Si substrate as spectrally sensitive absorbers to allow for light absorption from visible to SWIR.…”

“…NWs were etched to heights of 2 μm using the method we previously described ( Fig. 1a-b, [5]). It is important to note that the intrinsic section is fully embedded in the NWs.…”

High-performance silicon nanowire bipolar phototransistors

“…The miniaturization of semiconductor devices to the subwavelength scale has opened up new possibilities for creating faster, smaller, and more sensitive photodetectors. In recent years, there has been a growing interest in nanowire photodetectors based on Si, [1][2][3][4][5][6][7][8][9] Ge, 10,11 and various III-V [12][13][14] and II-VI 1,15 materials. In the simplest device structure, both ends of a single nanowire are connected to electrodes.…”

Harnessing the Interplay between Photonic Resonances and Carrier Extraction for Narrowband Germanium Nanowire Photodetectors Spanning the Visible to Infrared

“…We demonstrated color imaging using silicon nanowire photodetectors 19 . In other work, we demonstrated the tuning of dip features in the reflection spectra of germanium nanowire (Ge NW) arrays from visible to SWIR wavelengths 20 . Here, we demonstrate narrowband photodetectors with peaks in external quantum efficiency (EQE) spectra that can be tuned from visible to SWIR wavelengths.…”