Radiation Ionization Processes in Germanium and Silicon Crystals

“…In Si, where the creation energy per e − h þ pair is ϵ eh ¼ 3.8 eV, this is equivalent to ∼0.4 eV in electronic recoil energy, though it is a discrete energy scale [see Eq. (2)] and e − h þ pairs can be generated down to the band gap energy E gap ¼ 1.2 eV [22].…”

mentioning

confidence: 99%

First Dark Matter Constraints from a SuperCDMS Single-Charge Sensitive Detector

Agnese¹,

Aralis²,

Aramaki³

et al. 2018

Phys. Rev. Lett.

276

209

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“…The process becomes inefficient for NC exceeding 3 nm in diameter in the photon energy range of 2-3 times the band gap. PACS numbers: 78.67.Bf, 71.35.-y.Carrier multiplication is a process where several excitons are generated upon the absorption of a single photon in semiconductors [1]. Strict selection rules and competing processes in the bulk allow observation of CM only at energies larger than 5 times the band gap ( The theory of CM in bulk is based on the concept of impact ionization [15], by which the photon first creates an exciton, composed of the negative electron and positive hole, each having an effective mass depending on the band structure of the crystal.…”

mentioning

confidence: 99%

Distribution of Multiexciton Generation Rates in CdSe and InAs Nanocrystals

2008

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The distribution of rates of carrier multiplication (CM) following photon absorption is calculated for semiconductor nanocrystals (NCs). The NC electronic structure is described using a screened pseudopotential method known to give reliable description of NC excitons. The rates of biexciton generation are calculated using Fermi's golden rule with all relevant Coulomb matrix elements, taking into account proper selection rules. In CdSe and InAs NCs we find a broad distribution biexciton generation rates depending strongly on the exciton energy and size of the NC. The process becomes inefficient for NC exceeding 3 nm in diameter in the photon energy range of 2-3 times the band gap. PACS numbers: 78.67.Bf, 71.35.-y.Carrier multiplication is a process where several excitons are generated upon the absorption of a single photon in semiconductors [1]. Strict selection rules and competing processes in the bulk allow observation of CM only at energies larger than 5 times the band gap ( The theory of CM in bulk is based on the concept of impact ionization [15], by which the photon first creates an exciton, composed of the negative electron and positive hole, each having an effective mass depending on the band structure of the crystal. The lighter particle of the pair takes most of the kinetic energy and eventually looses part of this energy by creating additional charge carriers. For NCs, several theoretical approaches for describing CM have been proposed [4,6,[16][17][18][19]. Efros, Nozik and their co-workers [4,16] developed a time-dependent density matrix formalism taking into account the populations and coherences of single exciton coupled to a single biexciton state. Using this model, in conjunction with an effective mass theory, they developed a theory of impact ionization obtaining expression for the ratio of exciton to biexciton populations at steady states, which depend on the decay rate of the charged particle in the exciton into a trion. This approach treats a single trion neglecting the fact that the charged particle decays into a dense manifold of trions. Under such circumstance a rate approach might be more appropriate, describing the decay as an incoherent impact ionization process [17], similar to the treatment of the process in bulk.

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“…The active region of the laser with transverse electron beam pumping is usually arranged at a distance of several micrometers from the surface. It was shown as a result of numerous experimental investigations of impact ionization [4,5] that average energy 〈E〉 necessary for the formation of one pair of carriers under the effect of the primary electron is determined only by the band gap of semiconductor 〈E〉 ≈ 3E g . Therefore, electrons with an energy of several tens and hundreds of kilo electronvolts possess the deliberately excessive energy.…”

mentioning

confidence: 99%

Field injection of low-energy electrons into the ZnSe/CdSe/ZnSe heterostructure with the use of an ultra-high-vacuum tunneling microscope

et al. 2012

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In lasers with electron beam pumping, the semi conductor crystal transforms the energy of the acceler ated electron beam into the laser emission with a wavelength corresponding to the band gap of the used semiconductor. Pumping with the fast electron beam is a universal method of lasing in semiconductor mate rials with any band gap E g and any starting resistivity. Such lasers make it possible to generate optical pulses with a power of several tens of megawatts in a broad spectral range from the mid IR to near UV range.The main advantage of the lasers with electron beam pumping is in the absence of necessity of doping the used semiconductor materials. Elimination of requirements to p doping is especially essential for wide band gap semiconductor structures formed based on Group II-VI and III-V elements. Electron energy in electron beam pumping is relatively high, namely, 5-100 keV [1,2]. The necessity of using such energies is associated with low efficiency of penetra tion of the electron beam into the solid. Upon varying the energy of electrons from 10 to 200 keV, their effec tive penetration depth varies from 1 to 60 μm [3]. The active region of the laser with transverse electron beam pumping is usually arranged at a distance of several micrometers from the surface. It was shown as a result of numerous experimental investigations of impact ionization [4, 5] that average energy 〈E〉 necessary for the formation of one pair of carriers under the effect of the primary electron is determined only by the band gap of semiconductor 〈E〉 ≈ 3E g . Therefore, electrons with an energy of several tens and hundreds of kilo electronvolts possess the deliberately excessive energy.The use of high energy electrons causes the problems associated with carrier thermalization to equilibrium temperatures. This leads to nonuniform heating of the crystal lattice, appearance of local mechanical stresses, and overheating of the quasi equilibrium electron-hole plasma (which appears during pair Coulomb collisions) in the active region of the laser [3]. A decrease in the excessive energy of the electron beam eliminates the problems associated with the sub sequent thermalization and, as a consequence, leads to a decrease in the threshold current density. In recent time, a stable tendency to decreasing the pump elec tron beam energy is observed. The use of the miniature field electron source in [6] made it possible to fabricate compact lasers operating at beam energies of 7-10 keV in the near IR range at 90-300 K.In this work, we evaluated the efficiency of the use of the low voltage field electron emission for electron beam pumping. As the electron source, the metal probe of an LS SPM ultra high vacuum probe micro scope (OMICRON) is used. The probe of the ultra high vacuum scanning tunneling microscope (STM) is moved closer to the heterostructure under study to a distance of several nanometers. With the negative bias voltage of several volts supplied to the metal probe, field electron emission from the metal surface appears under the effect of...

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Radiation Ionization Processes in Germanium and Silicon Crystals

Cited by 54 publications

References 4 publications

First Dark Matter Constraints from a SuperCDMS Single-Charge Sensitive Detector

First Dark Matter Constraints from a SuperCDMS Single-Charge Sensitive Detector

Distribution of Multiexciton Generation Rates in CdSe and InAs Nanocrystals

Field injection of low-energy electrons into the ZnSe/CdSe/ZnSe heterostructure with the use of an ultra-high-vacuum tunneling microscope

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