A heavily doped germanium pyramid array for tunable optical antireflection in the broadband mid-infrared range

Son, Bongkwon; Shin, Sangho; Jin, Yuhao; Liao, Yikai; Zhao, Zhi‐Jun; Jeong, Jun‐Ho; Wang, Qijie; Wang, Xincai; Tan, Chuan Seng; Kim, Munho

doi:10.1039/d2tc00141a

Cited by 4 publications

(2 citation statements)

References 38 publications

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“…The short-length-scale orientation dependence of etch rates, leading to pyramidal structures on the 1-micron scale, has been reported [29][30][31]. At this length scale, the rates of i-MACE and the formation of pyramidal structures are dictated by the anisotropic etching of Ge crystalline facets.…”

Section: Resultsmentioning

confidence: 95%

“…Recent publications on applications of MACE to Ge photodetectors focus on creating closely spaced roughening features on the scale of a micron, close to the the wavelength of light for telecommunications [22,23]. Creation of periodic arrays of nanopyramids to reduce reflectivity has been demonstrated in the mid-infrared and beyond [29][30][31]. Lu et al used HF and H 2 O 2 as the etchant and silver (Ag) as the metal catalyst [22].…”

Section: Introductionmentioning

confidence: 99%

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Inverse metal-assisted chemical etching of germanium with gold and hydrogen peroxide

et al. 2022

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Metal-assisted chemical etching (MACE) is a ﬂexible technique for texturing the surface of semiconductors. In this work, we study the spatial variation of the etch proﬁle, the eﬀect of angular orientation relative to the crystallographic planes, and the eﬀect of doping type. We employ gold in direct contact with germanium as the metal catalyst, and dilute hydrogen peroxide solution as the chemical etchant. With this catalyst-etchant combination, we observe inverse-MACE, where the area directly under gold is not etched, but the neighboring, exposed germanium experiences enhanced etching. This enhancement in etching decays exponentially with the lateral distance from the gold structure. An empirical formula for the gold-enhanced etching depth as a function of lateral distance from the edge of the gold ﬁlm is extracted from the experimentally measured etch proﬁles. The lateral range of enhanced etching is approximately 10–20 µm and is independent of etchant concentration. At length scales beyond a few microns, the etching enhancement is independent of the orientation with respect to the germanium crystallographic planes. The etch rate as a function of etchant concentration follows a power law with exponent smaller than 1. The observed etch rates and proﬁles are independent of whether the germanium substrate is n-type, p-type, or nearly intrinsic.

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Section: Resultsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Inverse metal-assisted chemical etching of germanium with gold and hydrogen peroxide

et al. 2022

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Amorphous to Polycrystalline Phase Transition of In Situ Annealed Ge Films: Structural, Morphological, Optical, and Electrical Characteristics

Singh,

Gupta,

Aggarwal

2024

ChemistrySelect

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Radio Frequency (RF) sputtered germanium (Ge) thin films were deposited on glass substrate at in situ annealing temperatures of 400, 450, 500, 550, and 600 °C. X‐ray diffraction (XRD) and Raman spectroscopy revealed that the Ge films were initially amorphous but transformed to polycrystalline after annealing at 450 °C. Further annealing up to 600 °C resulted in improved crystallinity. Strain studies of the films using XRD and Raman showed compressive (out‐of‐plane) and tensile (in‐plane) strains, respectively, throughout all the annealing temperatures. The surface morphology of the films was recorded using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), which showed grain growth with annealing temperatures. The optical energy gap evaluated from absorption spectra for crystalline films decreased with annealing temperature, indicating improvement in crystallinity of films. The resistivity of the films deduced using current‐voltage measurements was found to decrease with annealing temperature, which can be attributed to enhancement in grain size. This study establishes a correlation between strain, grain size, optical energy gap, and electrical resistivity with temperature for Ge films deposited on glass substrates. Thus, the present study provides insights into variation in physical and electrical properties of films with in situ annealing temperature for their applicability in optoelectronic devices.

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Investigation of Doping Processes to Achieve Highly Doped Czochralski Germanium Ingots

Subramanian

Абросимов

Gybin

et al. 2023

J. Electron. Mater.

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Highly doped germanium (HD-Ge) is a promising material for mid-infrared detectors, bio-sensors, and other devices. Bulk crystals with a doping concentration higher than 1018 cm−3 would be desirable for such device fabrication technologies. Hence, an effective method needs to be developed to dope germanium (Ge) ingots in the Czochralski (Cz) growth process. In this study, a total of 5 ingots were grown by the Cz technique: two undoped Ge ingots as a reference and three doped ingots with 1018, 1019 , and 1020 atoms/cm3 respectively. To obtain a uniform p-type doping concentration along the crystal, co-doping of boron-gallium (B-Ga) via the Ge feed material was also attempted. Both B and Ga are p-type dopants, but with a large difference in their segregation behavior (contrary segregation profile) in Ge, and hence it is expected that the incorporation of dopants in the crystal would be uniform along the crystal length. The distribution of the dopants followed the Scheil-predicted profile. The etch pit density maps of the grown crystals showed an average dislocation density in the order of 105 cm−2. No increase in the overall etch pit count was observed with increasing dopant concentration in the crystal. The grown highly doped Ge crystals have a good structural quality as confirmed by x-ray diffraction rocking curve measurements.

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A heavily doped germanium pyramid array for tunable optical antireflection in the broadband mid-infrared range

Abstract: In this work, we report the heavily doped germanium (Ge) inverted pyramid array as a suitable candidate for tunable antireflection in mid-infrared (MIR) range. Inverted Ge pyramid structures are formed...

Cited by 4 publications

References 38 publications

Inverse metal-assisted chemical etching of germanium with gold and hydrogen peroxide

Inverse metal-assisted chemical etching of germanium with gold and hydrogen peroxide

Amorphous to Polycrystalline Phase Transition of In Situ Annealed Ge Films: Structural, Morphological, Optical, and Electrical Characteristics

Investigation of Doping Processes to Achieve Highly Doped Czochralski Germanium Ingots

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