Search query: Energy band splitting and high-order harmonic generation from a doped semiconductor

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abstract: We theoretically investigate the high order harmonic generation (HHG) from laser solid interaction in a doped semiconductor by solving the one dimensional time dependent Schrodinger equation within the single active electron model. The results show that the energy band of the valence and the low conduction band can be split into a small band in the doped semiconductor. The splitting band gap can be controlled by changing the depth of the potential well of the doped semiconductor, and the second HHG plateau can be enhanced. We also demonstrate the energy band structures in coordinate space with different numbers of dopant. Time dependent population imaging is used to illustrate the change of the splitting band gap with different depths of the potential well of the doped semiconductor.
author_names: Xue-Fei Pan

Tao Han

C L Xia

Tong-Tong Xu

Jingdong Zhang

Xueshen Liu
title: Energy band splitting and high order harmonic generation from a doped semiconductor
venue: Laser Physics Letters
year: 2019

abstract: We investigate the high order harmonic generation (HHG) in doped semiconductors. The HHG is simulated with the single electron time dependent Schr\"{o}dinger equation (TDSE) The results show that the high order harmonics in the second plateau generated from the doped semiconductors is about 1 to 3 orders of magnitude higher than those from the undoped semiconductor. The results are explained based on the analysis of the energy band structure and the time dependent population imaging. Our work indicates that doping can effectively control the HHG in semiconductor.
author_names: Tengfei Huang

Xiaosong Zhu

Liang Li

Xi Liu

Pengfei Lan

Peixiang Lu
title: High order harmonic generation of a doped semiconductor
year: 2017

abstract: We investigate the high order harmonic generation (HHG) in doped semiconductors. The HHG is simulated with the single electron time dependent Schrodinger equation (TDSE) The results show that the high order harmonics in the second plateau generated from the doped semiconductors is about 1 to 3 orders of magnitude higher than those from the undoped semiconductor. The results are explained based on the analysis of the energy band structure and the time dependent population imaging. Our work indicates that doping can effectively control the HHG in semiconductor.
author_names: Tengfei Huang

Xiaosong Zhu

Liang Li

Xi Liu

Pengfei Lan

Peixiang Lu
title: 2 3 O ct 2 01 7 High order harmonic generation of doped semiconductor
year: 2018

abstract: The development of new and inexpensive semiconductor electrodes that possess suitable band gap energies and band positions for solar water splitting is of great interest in the field of solar fuel production. In this study, n type Cu11V6O26 that has a band gap energy of 1.9 eV was produced as a pure, high quality photoanode, and its properties and stability for photoelectrochemical water splitting were systematically investigated in pH 9.2 and 13 solutions. As Cu11V6O26 photoanodes appeared to suffer from poor charge transport properties, Mo and W doping into the V site was also examined, which considerably improved the photocurrent generation of Cu11V6O26. The band gap energy, band edge positions, flatband potential, photocurrent generation, and photostability of pristine and doped Cu11V6O26 electrodes are discussed in comparison to elucidate the effect of Mo and W doping and to evaluate the promise and limitations of Cu11V6O26 as a photoanode for use in a water splitting photoelectrochemical cell.
author_names: Margaret A Lumley

Kyoung-Shin Choi
title: Investigation of Pristine and (Mo, W) Doped Cu11V6O26 for Use as Photoanodes for Solar Water Splitting
year: 2017

abstract: The wavelength scaling of the cutoff energy in solid high harmonic generation (HHG) is investigated theoretically by separating the contributions into the intraband and interband components. We find that, the cutoff energies of intraband and interband HHG exhibit the essentially different wavelength dependences. Specifically, the cutoff energy of the intraband HHG is wavelength independent, whereas the cutoff energy of the interband HHG depends linearly on the laser wavelength. Our results can uniformly interpret two current different wavelength scalings of the cutoff energy reported in previous researches. The fundamentally different wavelength scalings of the cutoff energy for intraband and interband HHG can be used to distinguish the two mechanisms. 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title: Wavelength scaling of the cutoff energy in the solid high harmonic generation
year: 2017

abstract: Abstract Hydrogen generation from photoelectrochemical (PEC) water splitting is on the forefront of clean energy generation landscape. The efficiency of PEC system is dependent on the engineering of semiconductors with tailored narrow band gap coupled with superior photoelectrochemical activity and desired stability vital for the commercialization of PEC water splitting cells. We report herein the study of vertically aligned Nb and N doped SnO2 nanotubes (NTs) i.e. (Sn0.95Nb0.05)O2:N NTs for PEC water splitting. (Sn0.95Nb0.05)O2 NTs was selected for co doping with nitrogen by systematic analysis of applied bias photon to current efficiency of various Nb doped SnO2 (x 0 0.1) compositions. Consequently, excellent photoelectrochemical stability and the highest efficiency of 4.1% is obtained for (Sn0.95Nb0.05)O2:N 600 NTs never observed for other known TiO2, ZnO, and Fe2O3 systems to date. Additionally, theoretical first principles study provides understanding of Nb and N co doping on the electronic structure and band gap of SnO2 semiconductor, further corroborating results of the experimental study.
author_names: Prasad Prakash Patel

Prashanth Jampani Hanumantha

Oleg I Velikokhatnyi

Moni Kanchan Datta

Bharat Gattu

James A Poston

Ayyakkannu Manivannan

Prashant N Kumta
title: Vertically aligned nitrogen doped (Sn,Nb)O2 nanotubes Robust photoanodes for hydrogen generation by photoelectrochemical water splitting
year: 2016

abstract: Ionization threshold in a semiconductor is determined through the value of band gap energy (Eg, 1 eV to 5 eV) which monitors the avalanche breakdown phenomenon of corresponding reverse biased p n junctions. Further the p n junction under avalanche breakdown can generate high frequency (hf) power (between 10 and 400GHz and beyond) in Impatt mode, as negative resistance oscillator, performance of which again depends on band gap energy of the semiconductor. Computer aided studies on breakdown and hf performance characteristics of flat DD (ppnn) Impatts based on conventional materials with moderate band gap energy Si, GaAs and InP having Eg=1.12, 1.36 and 1.26 eV respectively) as well as wide band gap semiconductors (ZnS, SiC and GaN, with respectively values of Eg =3.68, 2.9 and 3.4 eV) are presented. The p n junctions of materials having wide band gap energy needs sufficiently high reverse electric field/reverse bias voltage to initiate avalanche breakdown, as compared to the same for materials with low gap. For 3 micron pp nn type flat doped junction, the breakdown field and breakdown voltage for ZnS diode become 170 V/micron and 661 V respectively as against 40 V/micron and 72 V for corresponding Si junction. Similar trend has been observed for SiC, GaN and InP, GaAs diode junctions. The rf analysis of the corresponding Impatt diodes shows that the Device efficiency (21.1% and negative resistance (0.228 x 10 O.m) for 60 GHz (1 micron) ZnS DDRs are respectively around 1.9, 2.4 times of the values of the same parameters of corresponding Silicon DDR. The inherent avalanche noise associated with ZnS diode has been computed to be only 7% of the noise generated in Si Impatt diode. The performance of ZnS diode is also compared 230 Shankar P. Pati, Pravash R. Tripathy and Santosh K. Dash with diodes based on GaAs, InP, GaN and SiC diodes. The computed value of efficiency rf power output remains low, noise level becomes high for GaAs, InP, SiC and GaN devices compared to ZnS DDD. Computed values of rf power from 60 GHz Si, GaAs, InP, SiC, GaN and ZnS DDRs have been found respectively to be 18.9, 66.65, 119.95, 1532.7, 979.99 and 1987.4 W. RF power generation also have been investigated by considering respective diode area to be 50a, 10a, 5a,2a, and a where a is 10m for different frequency ranges (11 GHz 140GHz) for ZnS based IMPATTs which indicates similar trend of high rf power realization from ZnS DDDs in this entire frequency range. Indexing Terms: Band Gap Energy, ZnS, GaN, SiC, InP, GaAs, Si, Flat DDD, Impatt, mm power, Avalanche Noise. Introduction Ionization threshold in a semiconductor is determined through the value of band gap energy (normally the value of band gap energy, Eg, remains in the range of 0.66 eV to 5.1 eV for practical semiconductors) which monitors the avalanche breakdown phenomenon of reverse biased p n junctions based on the same semiconductor. Further reverse biased p n junction under avalanche breakdown can generate high frequency (hf) power (fundamental frequency ranges between 10 and 400 GHz) in impatt mode, as negative resistance oscillator, performance of which is supposed to depend on band gap energy of the semiconductor. Under harmonic mode the frequency can be still pushed to 1000 GHz, which is usually not achievable by any other solid state semiconductor device. Further advantage of impatt class of device is that the junction device can be fabricated from any semiconductor as the device physics is not typical to particular semiconductor. The negative resistance is produced due to combined phenomena of transit time delay and avalanche phase delay, making the total phase delay between rf current and voltage between p/2 and 3p/2. The efficiency and rf power output fall when the frequency is pushed to mm wave/submm wave bands. Research work is being carried out by different groups of scientists/engineers to enhance the efficiency and mm wave power from this class of device even at beyond mm wave frequencies. New materials are being studied and explored for impatt diodes with a view to achieve the above mentioned objectives. The indication from report of better microwave performance from GaAs and InP impatt over silicon diode due their higher band gap provides motive to study the device characteristics of wide gap semiconductor based impatt diodes vis a vis impatt diodes fabricated from narrow gap semiconductor. The authors have selected ZnS, SiC GaN (respective values of Eg =3.68, 2.9 and 3.4eV) as prospective wide band semiconductors and considered Si, InP GaAs (having Eg=1.12, 1.36 and 1.26 eV respectively) as moderate band gap semiconductors and compared breakdown as well as hf characteristics of p n junction impatts with above mentioned base semiconductors. The properties of ZnS impatt diodes are observed to excel over the rest. This has given reasons to the authors to provide due emphasis to ZnS as one Avalanche Breakdown Charecteristics of Wide 231 prospective material for high efficiency and high rf power generation associated with low noise. Since the device technology is now very advanced and a lot of experimental reports are available on Silicon Impatts, first the properties of ZnS Impatts are compared with those of Silicon diodes. A review of recent reports [1 4] on high field transport properties and ionization rate data in ZnS indicate some interesting features like very high value of electron ionization rate at electric field above 1.5x10 V/m and its sharp fall below this field. These properties are supposed to identify ZnS as a prospective material for impatt device. Flat doped ZnS impatt diodes (pp nn) have been analyzed for a wide range of doping/frequencies through use of a three phase generalized computer algorithm, which can be used to compute microwave/mm wave properties and also to estimate the generation of avalanche noise for any form of impatt represented in figure 1. The results have been compared with Si Impatts designed for corresponding frequencies. The results indicate high values of breakdown electric field (Em) and breakdown voltage (VB) for ZnS diode. The avalanche zone becomes localized leading to possible realization of optimum high efficiency (e 28% at 18 GHz) and enhanced value of diode negative resistance (Zr) High VB would make the diode capable of handling high power and high e and Zr help in producing high rf power. In addition the computed value of mean square avalanche noise voltage (NV) and Noise measure (NM) are observed to be lower by an order of magnitude compared to corresponding conventional devices based on common semiconductors. However, the advantages of ZnS impatts are observed to be moderated at frequencies beyond 140 GHz. Thus ZnS may prove to be a promising high Eg material for use in Impatt diode fabrication in order to realize high rf power with high e and low noise form X band to D band (10140 GHz) Analysis also has been carried out for Impatt diodes based on GaAs InP low band gap materials and SiC GaN wide band gap materials IMPATTs. A comparative account of the rf performance of the devices are presented in this paper which indicates possibility of high mm wave power generation associated with low noise from ZnS devices compared to Si, GaAs, InP, SiC and GaN based Impatts. 232 Shankar P. Pati, Pravash R. Tripathy and Santosh K. Dash Figure 1: Schematic Double Drift Structure of Impatt Diode. Theory and Simulation Method Extracting the values of electron ionization rate (a) at different electric field values [2] a usual exponential (a=a.exp b/Eg) as well as high order polynomial form (a=a0+a1E+a2E +a3E +anE of equations for a~E, are framed following usual curve fitting technique. The values of 'a' 'b' and g in the exponential form and those of a1 to a8 are determined/used for the high field and low field zones. The drift velocities are taken from [4] The electron and hole ionization rate are taken to be equal as ZnS is a very wide band gap semiconductor. Ionization rate, drift velocities and other material parameters for other semiconductors are taken from recent available experimental reports. A double iterative computer method to solve Poison, Carrier Continuity and space charge equations simultaneously subject to fulfillment of boundary conditions in electric field and carrier currents has been framed ensuring speedy convergence. The basic equations for DC analysis are, Poisson's equation, x E q (ND NA+p n) (1) and the current continuity equation is given by,
author_names: Shankar P Pati

Kaushik Dash

Pravash R Tripathy

Santosh Kumar Dash
title: Avalanche Breakdown Characteristics of Wide Band GaP vis a vis Low Band Gap Junctions and High RF Power/Low Noise Generation in ZnS DD IMPATTs
year: 2010

abstract: Abstract The generation of hydrogen and oxygen from the photocatalytic water splitting reaction under visible light is a promisingly renewable and clean source for H2 fuel. The transition metal oxide semiconductors (e.g. TiO2, WO3, ZnO, and ZrO2) are have been widely used as photocatalysts for the hydrogen generation. Because of safety, low cost, chemical inertness, photostability and other characteristics (bandgap, corrosion resistance, thermal and environmental stability) TiO2 is considered as a most potential catalyst of the semiconductors being investigated and developed. However, the extensive applications of TiO2 are hampered by its inability to exploit the solar energy of visible region. Other demerits are lesser absorbance under visible light, and recombination of photogenerated electron hole pairs. In this review, we focus on the all the possible reactions taking place at the catalyst during photo induced H2 from water splitting reaction, which is green and promising technology. Various parameter affecting the photocatalytic water splitting reactions are also studied. Predominantly, this review is focussed on bandgap engineering of TiO2 such as the upward shift of valence band and downward shift of conduction bands by doping process to extend its light absorption property into the visible region. Furthermore, the recent advances in this direction including various new strategies of synthesis, multiple doping, hetero junction, functionalization, perspective and future opportunities of non metals doped TiO2 based nanostructured photocatalysts for various photocatalytic applications such as efficient hydrogen production, air purification and CO2 reduction to valuable chemicals have been discussed.
author_names: Shivaraj B Patil

Patil S Basavarajappa

Nagaraju Ganganagappa

M S Jyothi

Anjanapura V Raghu

Kakarla Raghava Reddy
title: Recent advances in non metals doped TiO2 nanostructured photocatalysts for visible light driven hydrogen production, CO2 reduction and air purification
venue: International Journal of Hydrogen Energy
year: 2019

abstract: Summary form only given. High power ultrashort pulse lasers that operate around 2mm spectral region are of particular interest in expanding access to broadband coherent source options for the mid infrared spectral region. For example, such optical frequency comb generators can be utilized for real time, high sensitivity and high resolution detection of absorption features of molecular species present in the so called "molecular fingerprint" region. Amongst other potential implementations of 2 mm ultrafast lasers are free space optical communications, high harmonic generation, infrared pulsed laser ablation of polymer materials and surgery. Tm doped crystalline gain media could offer an attractive route towards the development of high power and efficient ultrashort pulse lasers for the 2 mm spectral region as alternatives to fiber [1] or semiconductor thin disk laser [2] approaches for which only rather limited average powers have been reported to date. For such purposes, Tm doped crystals having characteristic broadband and relatively homogeneous gain spectra extending beyond 2 mm (that avoid strong water absorption at l<;1950 nm) are required. Additionally, such media should support efficient cross relaxation processes in a Tm Tm manifold for efficient conversion of the pump radiation at 800 nm to laser emission around 2 mm and, as more general requirement, they possess good thermo mechanical properties.Here we report our recent results on femtosecond mode locking of Tm doped sesquioxides (Sc2O3, Lu2O3 and LuScO3) in the 2.0 2.1 mm region. The distinguishing features of these media include strong ground level Stark splitting that results in the emission spectra that extend beyond 2100 nm and superior thermo mechanical properties. All the experimental assessments were carried out with a Ti:sapphire pump laser (that produced up to 2.6 W at 796 nm) and an asymmetric, astigmatically compensated Z fold resonator which was configured with two high reflectivity (R 99.2% from 1770 to 2100 nm) folding mirrors having radii of curvature of 100 mm, an output coupling of 1.2% 2.3% or 4% and a SESAM. The SESAMs used for passive mode locking initiation and stabilization are based on an ion implanted InGaAsSb quantum well structure and characterised by an initial reflectivity of 99.5 98% in the 1950 2100 nm range. Pairs of IR grade fused silica or CaF2 prisms were used for the intracavity group velocity dispersion control. The shortest pulse duration of 105 fs was realised with a Tm:LuScO3 crystal operating around 2010 nm (Fig. 1) because it offered the broadest emission features [3]amongst all investigated gain media. The highest average power during mode locking of up to 0.75 W was achieved with the Tm:Lu2O3 ceramic gain medium at 2070 nm for a corresponding pulse duration of 382 fs. Continuous tunability was realized from 2030 nm to 2100 nm during the mode locking of the Tm:Lu2O3 laser where pulses as short as 300 fs were generated with an average power of 430 mW at around 2040 nm. The prospects of further power and energy scaling of femtosecond Tm doped sesquioxide lasers under highpower laser diode pumping will be discussed where the generation of yet shorter pulses can be expected when optimized SESAM devices or alternative broadband absorbers based on graphene are deployed.
author_names: Alexander a Lagatsky

Philipp Koopmann

Oleg L Antipov

C Tom A Brown

Gunter Huber

Wilson Sibbett
title: Femtosecond pulse generation with Tm doped sesquioxides
venue: 2013 Conference on Lasers Electro Optics Europe International Quantum Electronics Conference CLEO EUROPE/IQEC
year: 2013

abstract: Graphene quantum dots (GQDs) have emerged as a new group of quantum confined semiconductors in recent years, with possible applications as light absorbers, luminescent labels, electrocatalysts, and photoelectrodes for photoelectrochemical water splitting. However, their semiconductor characteristics, such as the effective band gap, majority carrier type, and photochemistry, are obscured by defects in this material. Herein, we use surface photovoltage spectroscopy (SPS) in combination with photoelectrochemical measurements to determine the parameters that are essential to the use of GQDs as next generation semiconductor devices and photocatalysts. Our results show that ordered GQDs (1 6 nm) behave as p type semiconductors, based on the positive photovoltage in the SPS measurements on Al, Au, and fluorine doped tin oxide substrates, and generate mobile charge carriers under excitation of defect states at 1.80 eV and under band gap excitation at 2.62 eV. Chemical reduction with hydrazine removes some defects and increases the effective band gap to 2.92 eV. SPS measurements in the presence of sacrificial electron donor and acceptors show that photochemical charge carriers can be extracted and promote redox reactions. A reduced GQDs photocathode supports an unprecedented photocurrent of 50 mA cm 2 using K3Fe(CN)6 as sacrificial electron acceptor. Additionally, while pristine GQDs do not photoreduce protons under visible light, hydrazine treated GQDs generate H2 from aqueous methanol under visible and UV light (0.04% quantum efficiency at 375 nm) without added co catalysts. These findings are relevant to the use of GQDs in photochemical and photovoltaic energy conversion systems.
author_names: Mauricio A Melo

Frank E Osterloh
title: Defect States Control Effective Band Gap and Photochemistry of Graphene Quantum Dots.
venue: ACS applied materials interfaces
year: 2018