Atomistic Mechanisms for the Thermal Relaxation of 
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-hyperdoped 
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Yang, Wenjie; Hudspeth, Quentin; Chow, Philippe K.; Warrender, Jeffrey M.; Ferdous, Naheed; Ertekin, Elif; Malladi, Girish; Akey, Austin; Aziz, Michael J.; Williams, James S.

doi:10.1103/physrevapplied.12.024015

Cited by 21 publications

(11 citation statements)

References 38 publications

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“…[80] for details). However, as expected, subsequent annealing at moderate temperatures resulted in a noticeable reduction in the sub-bandgap absorption due to Au moving off substitutional lattice sites where they are no longer electrically active [85]. In short, the results above strongly indicate that substitutional Au plays an important role in promoting NIR absorption and photoresponse in Au-hyperdoped Si.…”

Section: Optical and Photodevice Characterisationsupporting

confidence: 59%

Electrical and Optical Doping of Silicon by Pulsed-Laser Melting

Lim

Williams

2021

Micro

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Over four decades ago, pulsed-laser melting, or pulsed-laser annealing as it was termed at that time, was the subject of intense study as a potential advance in silicon device processing. In particular, it was found that nanosecond laser melting of the near-surface of silicon and subsequent liquid phase epitaxy could not only very effectively remove lattice disorder following ion implantation, but could achieve dopant electrical activities exceeding equilibrium solubility limits. However, when it was realised that solid phase annealing at longer time scales could achieve similar results, interest in pulsed-laser melting waned for over two decades as a processing method for silicon devices. With the emergence of flat panel displays in the 1990s, pulsed-laser melting was found to offer an attractive solution for large area crystallisation of amorphous silicon and dopant activation. This method gave improved thin film transistors used in the panel backplane to define the pixelation of displays. For this application, ultra-rapid pulsed laser melting remains the crystallisation method of choice since the heating is confined to the silicon thin film and the underlying glass or plastic substrates are protected from thermal degradation. This article will be organised chronologically, but treatment naturally divides into the two main topics: (1) an electrical doping research focus up until around 2000, and (2) optical doping as the research focus after that time. In the first part of this article, the early pulsed-laser annealing studies for electrical doping of silicon are reviewed, followed by the more recent use of pulsed-lasers for flat panel display fabrication. In terms of the second topic of this review, optical doping of silicon for efficient infrared light detection, this process requires deep level impurities to be introduced into the silicon lattice at high concentrations to form an intermediate band within the silicon bandgap. The chalcogen elements and then transition metals were investigated from the early 2000s since they can provide the required deep levels in silicon. However, their low solid solubilities necessitated ultra-rapid pulsed-laser melting to achieve supersaturation in silicon many orders of magnitude beyond the equilibrium solid solubility. Although infrared light absorption has been demonstrated using this approach, significant challenges were encountered in attempting to achieve efficient optical doping in such cases, or hyperdoping as it has been termed. Issues that limit this approach include: lateral and surface impurity segregation during solidification from the melt, leading to defective filaments throughout the doped layer; and poor efficiency of collection of photo-induced carriers necessary for the fabrication of photodetectors. The history and current status of optical hyperdoping of silicon with deep level impurities is reviewed in the second part of this article.

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Section: Optical and Photodevice Characterisationsupporting

confidence: 59%

Electrical and Optical Doping of Silicon by Pulsed-Laser Melting

Lim

Williams

2021

Micro

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“…Although Au Ge has the lowest formation energy, the formation of the other defects remains possible. For example, despite its high energy, Au i,tetr may form via kickout or dissociative mechanisms, as believed to occur for Si:Au upon thermal annealing [44]. In addition, Au i -2V can form when a substitutional Au and monovacancy are placed side by side and allowed to relax; the Au atom is attracted towards the vacancy resulting in the lattice distortion as shown in Fig.…”

Section: B Defect Energeticsmentioning

confidence: 99%

Carrier Dynamics and Absorption Properties of Gold-Hyperdoped Germanium: Insight Into Tailoring Defect Energetics

et al. 2021

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Hyperdoping germanium with gold is a potential method to produce room-temperature shortwavelength-infrared radiation (SWIR; 1.4-3.0 μm) photodetection. We investigate the charge carrier dynamics, light absorption, and structural properties of gold-hyperdoped germanium (Ge:Au) fabricated with varying ion implantation and nanosecond pulsed laser melting conditions. Time-resolved terahertz spectroscopy (TRTS) measurements show that Ge:Au carrier lifetime is significantly higher than that in previously studied hyperdoped silicon systems. Furthermore, we find that lattice composition, sub-bandgap optical absorption, and carrier dynamics depend greatly on hyperdoping conditions. We use density functional theory (DFT) to model dopant distribution, electronic band structure, and optical absorption. These simulations help explain experimentally observed differences in optical and optoelectronic behavior across different samples. DFT modeling reveals that substitutional dopant incorporation has the lowest formation energy and leads to deep energy levels. In contrast, interstitial or dopant-vacancy complex incorporation yields shallower energy levels that do not contribute to sub-band-gap light absorption and have a small effect on charge carrier lifetimes. These results suggest that it is promising to tailor dopant incorporation sites of Ge:Au for SWIR photodetection applications.

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“…While recent sub-band-gap photodetection studies have focused on Si, we work with Ge because of its higher carrier mobility [18,[25][26][27][28]. Previous studies of dopantmediated Ge photodetectors incorporating various dopants (S, Te, Zn, B, Cu, Cd, Zn, Au) through various doping methods have reported sub-band-gap responses only at low temperature, which is impractical for many SWIR applications [27][28][29][30][31]. We select Au as a dopant because Ge:Au has several properties that make it promising for a dopantmediated sub-band-gap photodetector.…”

Section: Introductionmentioning

confidence: 99%

“…We select Au as a dopant because Ge:Au has several properties that make it promising for a dopantmediated sub-band-gap photodetector. Au is a deep-level dopant and, relative to Ge with shallow-level dopants [32,33], Ge:Au demonstrates a lower thermal ionization at room temperature, reducing background free-carrier concentrations and improving device signal-to-noise ratios [27,28]. Among deep-level Ge dopants, Au uniquely has self-compensating defect levels [34] (see Fig.…”

Section: Introductionmentioning

confidence: 99%

“…These studies, primarily carried out in the 1950s-1970s, used conventional near-equilibrium doping methods that did not produce doping concentrations above the Ge:Au solubility limit (2.8 × 10 16 cm −3 ) [23,27]. Consequently, these Ge:Au photodetectors have a very low sub-band-gap absorption coefficient (α ≈ 0.1 cm −1 ) [27,28,35], and at room-temperature the background freecarrier concentration overwhelms the photosignal [30]. Such detectors, therefore, only operate under cooled conditions, typically between 4 and 78 K. Here, we show that hyperdoped Ge:Au has fundamentally different properties from those of conventional Ge:Au, namely, a much larger sub-band-gap absorption coefficient comparable to that of direct-band-gap semiconductors and room temperature sub-band-gap SWIR photodetection [38].…”

Section: Introductionmentioning

confidence: 99%

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Gold-Hyperdoped Germanium with Room-Temperature Sub-Band-Gap Optoelectronic Response

et al. 2020

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Short-wavelength-infrared (SWIR; 1.4-3.0 µm) photodetection is important for various applications. Inducing a low-cost silicon-compatible material, such as germanium, to detect SWIR light would be advantageous for SWIR applications compared with using conventional (III-V or II-VI) SWIR materials. Here, we present a scalable nonequilibrium method for hyperdoping germanium with gold for dopantmediated SWIR photodetection. Using ion implantation followed by nanosecond pulsed laser melting, we obtain a single-crystal material with a peak gold concentration of 3 × 10 19 cm −3 (10 3 times the solubility limit). This hyperdoped germanium has fundamentally different optoelectronic properties from those of intrinsic and conventionally doped germanium. This material exhibits sub-band-gap absorption of light up to wavelengths of at least 3 µm, with a sub-band-gap optical absorption coefficient comparable to that of commercial SWIR photodetection materials. We show that germanium hyperdoped with gold exhibits sub-band-gap SWIR photodetection at room temperature, in contrast with previous doped-germanium photodetector studies, which only show a low-temperature response. This material is a potential pathway to low-cost room-temperature silicon-compatible SWIR photodetection.

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Atomistic Mechanisms for the Thermal Relaxation of Au -hyperdoped Si

Cited by 21 publications

References 38 publications

Electrical and Optical Doping of Silicon by Pulsed-Laser Melting

Electrical and Optical Doping of Silicon by Pulsed-Laser Melting

Carrier Dynamics and Absorption Properties of Gold-Hyperdoped Germanium: Insight Into Tailoring Defect Energetics

Gold-Hyperdoped Germanium with Room-Temperature Sub-Band-Gap Optoelectronic Response

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