Ultrafast high-field transport in GaAs: direct observation of quasi-ballistic electron motion, impact ionization and avalanche multiplication

Betz, M.; Trumm, S.; Sotier, F.; Leitenstorfer, Alfred; Schwanhäußer, Anja; Eckardt, M.; Schmidt, O.; Malzer, S.; Döhler, G. H.; Hanson, M.; Driscoll, D. C.; Gossard, A. C.

doi:10.1088/0268-1242/19/4/058

Cited by 3 publications

(5 citation statements)

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“…In the present technique, we exploit SPPs for generating more carriers close to subwavelength normal metal electrodes embedded in a photoconductor layer sandwiched between two Distributed Bragg Reflectors (DBR) that form a Fabry-Perot (FP) cavity. When coupled with velocity overshoot phenomenon reported in many photoconductor materials [12,16,17,18,19,20], t tr of majority of carriers is reduced to < 1 ps, i.e., t tr ≤ f −1 . For efficient use of SPPs, it is desirable to have thin (∼10 nm) normal metal lines with subwavelength features distributed throughout the active volume (Fig 1a) in a manner that would collectively enhance the optical field intensity in the vicinity of the metal lines.…”

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confidence: 92%

“…When coupled with velocity overshoot phenomenon reported in many photoconductor materials [12,16,17,18,19,20], t tr of majority of carriers is reduced to < 1 ps, i.e., t tr ≤ f −1 . For efficient use of SPPs, it is desirable to have thin (∼10 nm) normal metal lines with subwavelength features distributed throughout the active volume (Fig 1a) in a manner that would collectively enhance the optical field intensity in the vicinity of the metal lines.…”

mentioning

confidence: 93%

“…These carriers generated predominantly in the near field enhancement region, transit through nonuniform dc fields in the 5 to 90 kV/cm range. It should be noted that t onset = 100 fs is considerably lower than the theoretical limit of ballistic motion in GaAs for this field strength range [16]. For t tr ≥ t onset , electron motion is approximated by qasiballistic transport with time dependent velocity distribution similar to ref.…”

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confidence: 93%

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Enhancing the photomixing efficiency of optoelectronic devices in the terahertz regime

Pilla

2007

Applied Physics Letters

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A method to reduce the transit time of majority of carriers in photomixers and photo detectors to < 1 ps is proposed. Enhanced optical fields associated with surface plasmon polaritons, coupled with velocity overshoot phenomenon results in net decrease of transit time of carriers. As an example, model calculations demonstrating > 280× (or ∼2800 and 31.8 µW at 1 and 5 THz respectively) improvement in THz power generation efficiency of a photomixer based on Low Temperature grown GaAs are presented. Due to minimal dependence on the carrier recombination time, it is anticipated that the proposed method paves the way for enhancing the speed and efficiency of photomixers and detectors covering UV to far infrared communications wavelengths (300 to 1600 nm).Recent experimental observation of extraordinary optical transmission through a normal metal film having subwavelength holes[1] has generated intense interest in harnessing the underlying physics for photonic applications. It is widely believed that quasi two-dimensional electromagnetic excitations tightly bound to the metal surface known as Surface Plasmon Polaritons (SPPs) are responsible for the observed near field enhancement of the optical radiation. Exponential decay of field components arising from SPPs (penetrating ∼100, ∼10 nm in dielectric and metal respectively), make them highly attractive for miniature photonic circuits and devices [2]. Currently, several potential applications of SPPs are being explored including wave guiding [3] and near-field microscopy [4]. However, application of SPPs to enhance the speed and efficiency of photo detectors or photomixers has not been attempted due to the complexity of underlying physics and optimal device designs involving complicated dielectric-metal structures.In this letter we propose a simple interdigitated metal structure embedded in a suitable semiconductor material to harness SPPs for improving the speed and efficiency of photomixers and detectors. Such a device can be realized with the existing material growth techniques [5]. As an example, we demonstrate via model calculations, significant (> 280×) improvement in the efficiency of a THz photomixer based on Low Temperature grown GaAs (LT-GaAs). Microwave to THz radiation sources in the 0.1 to 10 THz are being extensively studied for their application in communications, medical imaging, and spectroscopy [6,7,8,9,10]. For many applications-compact, narrow-linewidth, widely tunable continuous wave sources are necessary. In particular, to be used as a local oscillator in communications systems the THz source should produce stable output power > 10 µW [8,11]. Among the various techniques being pursued [6,8,11,12,13] electrical down conversion of optical microwave sources in a suitable photomixer [6,11,12] are appealing due to the easy availability of tunable, narrow-linewidth, and stable solid state lasers. However, until now the output power from these photomixers is limited to < 10 µW in the cru- . When the top and bottom interdigitated structures in (b) are con...

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confidence: 92%

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confidence: 93%

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confidence: 93%

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Enhancing the photomixing efficiency of optoelectronic devices in the terahertz regime

Pilla

2007

Applied Physics Letters

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“…Contrary, in semiinsulating (SI)-GaAs or SI-InGaAs ballistic transport is evident and consequently velocity overshoot. Ballistic electron transport in GaAs THz-emitters has been studied by Monte-Carlo simulations [22] and pump and probe experiments [23]. Furthermore, it has been shown that GaAs/AlGaAs p-i-n heterostructures are efficient pulsed THz emitters, even though they were not designed for ballistic transport [24].…”

Section: Introductionmentioning

confidence: 99%

Terahertz generation with ballistic photodiodes under pulsed operation

Muller-Landau

Malzer

Weber

et al. 2018

Semicond. Sci. Technol.

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We investigate high field and ballistic carrier transport in a 1.55 μm photomixing device based on pin-diodes by time resolved terahertz (THz) spectroscopy. The device consists of 3 stacked In(Al)GaAs pin diodes (n-i-pn-i-p superlattice) attached to a broadband logarithmic-periodic antenna. Each pin diode is optimized for exhibiting ballistic transport and a reduced transit time roll-off. Ballistic transport signatures could be confirmed directly in these experiments. The data are compared with results from continuous-wave experiments and from simulations both supporting our theoretical expectations. It is demonstrated that n-i-pn-i-p superlattice photomixers are also efficient THz emitters under pulsed operation, showing a maximum THz field strength of ∼0.5 V cm -1 (peak to peak) at 30 mW average optical power.

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“…3 Recently, the dynamics of carrier multiplication due to impact ionization has been studied experimentally on ultrashort time scales in Al x Ga 1−x As diodes. 4 The microscopic description of this extreme nonequilibrium process remains a demanding task.…”

Section: Introductionmentioning

confidence: 99%

Ab initioimpact ionization rate in GaAs, GaN, and ZnS

2005

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We have performed extensive ab initio band structure calculations within density functional theory using an exact exchange formalism with a local density approximation for correlations. The wave-vector-dependent impact ionization rate is determined for GaAs, GaN, and ZnS. A strong asymmetry of the microscopic scattering rate as well as a pronounced influence of the band structure is found. We present also energy-averaged impact ionization rates which can be used in ensemble Monte Carlo simulations of high-field electron transport in these materials.

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Ultrafast high-field transport in GaAs: direct observation of quasi-ballistic electron motion, impact ionization and avalanche multiplication

Cited by 3 publications

References 14 publications

Enhancing the photomixing efficiency of optoelectronic devices in the terahertz regime

Enhancing the photomixing efficiency of optoelectronic devices in the terahertz regime

Terahertz generation with ballistic photodiodes under pulsed operation

Ab initioimpact ionization rate in GaAs, GaN, and ZnS

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