Intervalence Band Research Articles

1.5 µm wavelength NPN-type photonic-crystal surface-emitting laser exceeding 100 mW.

A 1.5 µm laser diode has applications in eye-safe light detection and ranging (LiDAR) and optical communications via photonic integrated circuits. Photonic-crystal surface-emitting lasers (PCSELs) have lens-free applications in compact optical systems because of narrow beam divergences (<1 degree). However, the output power has still been less than 1 mW for 1.5 µm PCSELs. For higher output power, one approach is suppression of p-dopant Zn diffusion in the photonic crystal layer. Therefore, n-type doping was used for the upper crystal layer. Moreover, an NPN-type PCSEL structure was proposed to reduce intervalence band absorption in the p-InP layer. Here, we demonstrate a 1.5 µm PCSEL with 100 mW output power, which exceeds previous reported values by two orders of magnitude.

Probing Intervalence Band Coupling via High‐Harmonic Generation in Binary Zinc‐Blende Semiconductors

A systematic microscopic theory is presented for high‐harmonic generation in III–V semiconductors that are excited by strongly detuned high‐intensity electromagnetic pulses. As a mechanism for the appearance of even harmonic orders, the quantum interference of different transition paths is analyzed. For the binary zinc‐blende semiconductors, InAs, InP, and GaAs, the intensity ratio between even‐ and odd‐order harmonic emission depends on the strength of the respective intervalence band dipole coupling. However, the large intervalence band dipole in InP leads to even and odd harmonics of similar intensity, no or only very minor even‐order emission due to quantum interference is predicted for InAs where the fundamental transition is strongly favored over intervalence band transitions.

Impact of quantum dot parameters on the performance of p-type quantum dot infrared photodetectors

In this work, the impact of the quantum dot parameters, including dot size, and material composition on the optoelectronic performance of quantum dot infrared photodetectors (QDIPs) is systematically studied. The QDIP is based on the intra-valence band transitions in Zn 1-x Cd x Se QDs. The eigen energies and wavefunction of the hole states are computed under the framework of the multi-band k.p model. The obtained electronic structure is further utilized to calculate the dark current density, responsivity, and detectivity of QDIPs. An increase in CdSe content markedly reduces the dark current density as well as improves the responsivity. As a result, detectivity enhances significantly. Raising the QD size also brings enhancement in the detectivity. Moreover, peak response wavelength depends on the CdSe content and dot dimensions. These results might provide new directions for the development of p-type II-VI QDs based QDIP. • Infrared photodiode based on the intervalence band absorption has been studied. • Strain dependent multiband effective mass k.p model is used to compute the electronic structure of QDs. • Higher CdSe content and larger quantum dot yields better optoelectronic performance. • The Peak response wavelength is quite sensitive to the CdSe content.

Modeling of a SiGeSn quantum well laser

We present comprehensive modeling of a SiGeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers. We combine experimental material data obtained over the last few years with k · p theory to adapt transport, optical gain, and optical loss models to this material system (drift-diffusion, thermionic emission, gain calculations, free carrier absorption, and intervalence band absorption). Good consistency is obtained with experimental data, and the main mechanisms limiting the laser performance are discussed. In particular, modeling results indicate a low non-radiative lifetime, in the 100 ps range for the investigated material stack, and lower than expected Γ-L energy separation and/or carrier confinement to play a dominant role in the device properties. Moreover, they further indicate that this laser emits in transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge, this is the first comprehensive modeling of experimentally realized SiGeSn lasers, taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new (Si)GeSn laser device concepts.

Gold-Cage Perovskites: A Three-Dimensional AuIII-X Framework Encasing Isolated MX63- Octahedra (MIII = In, Sb, Bi; X = Cl-, Br-, I-).

The Cs8AuIII4MIIIX23 (M = In3+, Sb3+, Bi3+; X = Cl-, Br-, I-) perovskites are composed of corner-sharing Au-X octahedra that trace the edges of a cube containing an isolated M-X octahedron at its body center. This structure, unique within the halide perovskite family, may be derived from the doubled cubic perovskite unit cell by removing the metals at the cube faces. To our knowledge, these are the only halide perovskites where the octahedral sites do not bear an average 2+ charge. Charge compensation in these materials requires a stoichiometric halide vacancy, which is disordered around the Au atom at the unit-cell corner and orders when the crystallization is slowed. Using X-ray crystallography, X-ray absorption spectroscopy, and pair distribution function analysis, we elucidate the structure of this unusual perovskite. Metal-site alloying produces further intricacies in this structure, which our model explains. Compared to other halide perovskites, this class of materials shows unusually low absorption onset energies ranging between ca. 1.0 and 2.4 eV. Partial reduction of Au3+ to Au+ affords an intervalence charge-transfer band, which redshifts the absorption onset of Cs8Au4InCl23 from 2.4 to 1.5 eV. With connected Au-X octahedra and isolated M-X octahedra, this structure type combines zero- and three-dimensional metal-halide sublattices in a single material and stands out among halide perovskites for its ordering of homovalent metals, ordering of halide vacancies, and incorporation of purely trivalent metals at the octahedral sites.

Design optimization of tensile-strained SiGeSn/GeSn quantum wells at room temperature

A direct bandgap can be engineered in Ge-rich group-IV alloys by increasing Sn content and by introducing tensile strain in GeSn. Here, we combine these two routes in quantum well (QW) structures and systematically analyze the properties of SiGeSn/GeSn quantum wells for a range of Sn content, strain, and well width values, within realistic boundaries. Using the k⋅p method, and including L-valley within the effective mass method, we find that 13–16 nm is a preferred range of well widths to achieve high gain for tensile-strained SiGeSn/GeSn quantum wells. Within the range of the well widths, a loss ridge caused by inter-valence band absorption and free carrier absorption is found in the region of parameter space where Sn content and strain in the well are related as Sn(%)≈−7.71εxx(%)+17.13. Limited by a practical strain boundary of 1.7%, for a 14 nm quantum well, we find that 7.5±1% Sn and 1±0.2% strain is a promising combination to get a good net gain for photon transition energy higher than ∼0.42 eV. A maximum utilization of strain is preferred to obtain the best gain with lower energies (&amp;lt;0.42 eV). By comparing these designs with a compressive strain example, an engineered tensile structure shows a better performance, with a low threshold current density (1.42 kA/cm2). Finally, the potential benefit of p-doping of the tensile-strained GeSn QW is also discussed.

GeSn optical gain and lasing characteristics modelling

With recent demonstrations of lasing, germanium-tin (GeSn) stands out as a promising candidate for the integration of a low threshold, room temperature monolithic laser source in silicon (Si) photonics. The impact of physical properties, such as energy band structure, crystal quality, and cavity loss on lasing performances (i.e., lasing threshold and maximal lasing temperature) has to be better understood, however. In this work, we calculate the theoretical band-to-band net gain for relaxed, [100] uniaxial, and (100) biaxial tensile-strained GeSn. We show that the band-to-band net gain depends not only on the interband gain introduced by the transition between valence bands and conduction bands, but also on the intervalence band absorption between the valence bands. Both approaches, GeSn with high Sn concentration and/or with high tensile strain, can yield a band-to-band net gain at room temperature. Then, the integration of another source of absorption---free carrier absorption---will be discussed. Finally, from the simulation of GeSn lasing characteristics, we show the important role the crystal quality has on the lasing threshold. Based on the results, we suggest using GeSn with low/medium Sn concentrations, under very high [100] uniaxial or (100) biaxial tensile strain, to obtain a low threshold, room temperature lasers.

First-principles study on composition-dependent properties of quaternary InP1−x−yNxBiy alloys

The content of bismuth and nitrogen can strongly affect the physical properties of III–V semiconductors and have a decisive impact on their performance in applications. Using first-principles calculations, we systematically study the geometry, electronic and optical properties of [Formula: see text] aligned in special quasirandom structures (SQS). The incorporation of a small amount of N and Bi can effectively tune the band gap of pristine InP. For the same number of P atoms being substituted, co-doping mode reduced the bond length disparity and the corresponding formation energy was also smaller than that of only nitrogen doped. Since the bismuth doped increases spin-orbit splitting energy [Formula: see text], the Auger recombination and intervalence band absorption (IVBA) processes are found to be suppressed for quaternary [Formula: see text] (4.40 [Formula: see text]m), [Formula: see text] (12.04 [Formula: see text]m) and [Formula: see text] (9.12 [Formula: see text]m) alloys, which provides new feasibility in the future mid-wavelength infrared and long-wavelength infrared (MWIR/LWIR) device applications.

RAMAN STUDIES OF BIS(PHENYLTERPYRAZINE)IRON(II) AND SUPRAMOLECULAR SPECIES WITH PENTACYANIDOFERRATE(II) IONS

The chemistry and spectroscopy of the iron(II) phenylterpyrazine complex, [Fe(phtpz)2]2+, were investigated in comparison with the analogous phenylterpyridine species, Fe(phtpy)2]2+, and the results indicated a strong electronic delocalization on the Fe(II) terimine chromophore encompassing the lateral pyrazyl groups. The delocalized nature of the molecular orbitals involved in the electronic excitation precluded a direct assignment of the pyridine and pyrazine vibrations in the complex. However, the capability of the terpyrazine complex to bind transition metal ions, such as the [Fe(CN)5]3- species, allowed to generate pentanuclear complexes displaying characteristic charge-transfer and resonance Raman spectra, revealing the pyrazine vibrations in the complex. The [Fe(CN)5]3- containing species also yielded polymeric compounds in presence of transition metal ions, exhibiting intervalence transfer bands and chemical similarities with the Prussian Blue complex.

Sandwich double-decker Er(iii) and Yb(iii) complexes containing naphthalocyanine moiety: synthesis and investigation of the effect of a paramagnetic metal center.

Novel heteroleptic Er(iii) and Yb(iii) naphthalocyaninato-phthalocyaninates containing an octa-phenyl or octa-phenoxysubstituted naphthalocyanine deck were synthesised and identified by 1H NMR, EPR and high resolution MALDI-TOF/TOF mass spectrometry. Direct synthesis of novel homoleptic Yb(iii) bis (octa-phenylnaphthalocyaninate) was carried out. Downfield lanthanide induced shifts of the aromatic protons in target compounds were observed compared with the corresponding diamagnetic Lu(iii) complexes. In the near-IR absorption spectra, an increase in ionic radius from Lu(iii) to Er(iii) resulted in a bathochromic shift of the intervalence band up to 1473 nm. This work presents the first experimental EPR study of Yb(iii) bis naphthalocyaninate, where a set of magnetic parameters and properties (including spin, magnitude and sign of magnetic anisotropy parameter D, increased splitting in a crystal field, ferromagnetic f-π interaction etc.) were determined and interpreted by both EPR and SQUID techniques and supported by theoretical considerations.

Simultaneous measurement of infrared absorption coefficient of Carbon doped Al0.33Ga0.67As thin film and thermal boundary resistance between thin film and heavily Zn doped GaAs substrate using spectrally-resolved modulated photothermal infrared radiometry

In this paper, we investigated C doped Al0.33Ga0.67As thin film epitaxially grown on a Zn-doped GaAs substrate using spectrally resolved modulated photothermal infrared radiometry (SR-PTR). We assumed that thermal conductivity and diffusivity of the thin layer are known and estimate values of the infrared absorption coefficient of the thin layer and the thermal boundary resistance of the interface between the thin layer and the substrate. We found out that the thermal boundary resistance is two orders of magnitude greater than thermal boundary resistance of studied recently undoped AlGaAs/GaAs sample. We attribute this effect to formation of quasi 2-dimensional hole gas due to modulation doping. Finally, the infrared absorption coefficient of the thin layer decreases with increasing wavelength due to inter-valence band absorption. We found out that with increasing infrared absorption coefficient of the thin film, the sensitivity of the method for estimation of the infrared absorption coefficient increases, while the estimation error decreases.

Ultrafast nonlinear travel of hot carriers driven by high-field terahertz pulse

We aim to generate high-intensity terahertz (THz) electric fields and study nonlinear phenomena in GaAs and graphene to investigate their applications. To obtain a high-efficiency intense THz field, we employ the tilted pump-pulse front technique using a LiNbO3 crystal. With this technique, we obtain a THz field strength of over 300 kV cm−1. We investigate the hot-carrier dynamics in n- and p-type GaAs driven by high-field THz pulses. Although both samples show similar carrier concentrations, the nonlinear THz responses show different trends. Owing to hot-carrier generation, intervalley scattering is dominant in n-type GaAs, and intervalence band scattering is the main cause in p-type GaAs. In addition, we study the hot-carrier dynamics in graphene with the grain-size dependency. Although graphene has the same Fermi level regardless of the grain size, the THz responses are different for large- and small-grained graphene: charged impurity scattering in large-grained graphene and defect scattering in small-grained graphene. From these results, our study provides insights into high-speed electronics applications.

K ⋅ p calculations of bismuth induced changes in band structure of InN1−xBix, GaN1−xBix and AlN1−xBix alloys

Valence band anticrossing (VBAC) model is used to investigate band structure of InN[Formula: see text]Bi[Formula: see text], GaN[Formula: see text]Bi[Formula: see text] and AlN[Formula: see text]Bi[Formula: see text] for the purpose of optimal performance group-III nitride related devices. Obvious reduction in band gap and increase in spin–orbit splitting energy are founded by doping dilute concentration of bismuth in all these III-N material. The band gap of GaN[Formula: see text]Bi[Formula: see text] and AlN[Formula: see text]Bi[Formula: see text] show a step change, and this can be explained by the special position relation between of Bi impurity energy level with corresponding host’s band offsets. We also show how bismuth may be used to form alloys by finding the doping region [Formula: see text] which can provide a means of suppressing non-radiative CHSH (hot-hole producing) Auger recombination and inter-valence band absorption. For InN[Formula: see text]Bi[Formula: see text], bismuth concentration beyond 1.25% is found to be corresponding to the range of [Formula: see text] and it shows a continuous adjustable band gap from 0.7 eV to zero. This may make InN[Formula: see text]Bi[Formula: see text] a potential candidate for near or mid-infrared optoelectronic applications.

Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand.

An iron(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM4-), (NEt4)2[FeIII(DTTM)Cl] (1), was synthesized and characterized by crystallographic, spectroscopic, and electrochemical methods. Complex 1 has a square-pyramidal structure in the S = 3/2 spin state. The complex exhibited two reversible redox waves at +0.36 and +0.68 V (vs SCE) in the cyclic voltammogram measured in CH2Cl2 at room temperature. The stepwise oxidation of 1 using chemical oxidants allowed us to observe clear and distinct spectral changes with distinct isosbestic points for each step, in which oxidation occurred at the phenylenediamido moiety rather than the iron center. One-electron oxidation of 1 by 1 equiv of [RuIII(bpy)3](ClO4)3 (bpy = 2,2'-bipyridine) in CH2Cl2 afforded square-pyramidal (NEt4)[Fe(DTTM)Cl] (2), which was in the S = 1 spin state involving a ligand radical and showed a slightly distorted square-pyramidal structure. Complex 2 showed an intervalence charge-transfer band at 900 nm, which was assigned on the basis of time-dependent density functional theory calculations, to indicate that the complex is in a class IIA mixed-valence ligand-radical regime with Hab = 884 cm-1. Two-electron oxidation of 1 by 2 equiv of [(4-Br-Ph)3N•+](SbCl6) in CH2Cl2 afforded two-electron-oxidized species of 1, [Fe(DTTM)Cl] (3), which was in the S = 1/2 spin state; complex 3 exhibited a distorted square-pyramidal structure. X-ray absorption near-edge structure spectra of 1-3 were measured in both CH3CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and Mössbauer spectra of 1-3 showed almost identical isomer shifts and quadruple splitting parameters, indicating that the iron centers of the three complexes are intact to be in the intermediate-spin iron(III) state. Thus, in complexes 2 and 3, it is evident that antiferromagnetic coupling is operating between the unpaired electron(s) of the ligand radical(s) and those of the iron(III) center.

Relationship between the Fano asymmetry parameter and time-domain spectra studied by time-resolved measurement of carriers and phonons in p -type Si

We performed time-resolved reflectivity measurements in $p$-type Si to study the Fano asymmetry parameter as a function of time-domain parameters. We observed a fast decay of intervalence band transitions, and slow decay of optical phonons, which respectively correspond to the continuum and discrete states. The experimental results revealed that the initial phase of the discrete state and the ratio of the relative transition amplitude between the discrete and continuum states affect the Fano asymmetry parameter. We derived an equation for the Fano asymmetry parameter as a function of the time-domain parameters that explained the experimental results. The present study indicates how the Fano asymmetry parameter is controlled by the time-domain parameters.

Progress Toward III–V Bismide Alloys for Near- and Midinfrared Laser Diodes

Bismuth-containing III–V alloys open-up a range of possibilities for practical applications in semiconductor lasers, photovoltaics, spintronics, photodiodes, and thermoelectrics. Of particular promise for the development of semiconductor lasers is the possibility to grow GaAsBi laser structures such that the spin–orbit splitting energy ( $\Delta _{{\text{SO}}}$ ) is greater than the bandgap ( $E_{g}$ ) in the active region for devices operating around the telecom wavelength of 1.55 μ m, thereby suppressing the dominant efficiency-limiting loss processes in such lasers, namely Auger recombination and intervalence band absorption. The $\Delta _{{\text{SO}}}\,> \,E_{g}$ band structure is present in GaAsBi alloys containing > 10% Bi, at which composition the alloy bandgap is close to 1.55 μ m on a GaAs substrate making them an attractive candidate material system for the development of highly efficient, uncooled GaAs-based lasers for telecommunications. Here, we discuss progress toward this goal and present a comprehensive set of data on the properties of GaAsBi lasers including optical gain and absorption characteristics and the dominant carrier recombination processes in such systems. Finally, we briefly review the potential of GaAsBiN and InGaAsBi material systems for near- and midinfrared photonic devices on GaAs and InP platforms, respectively.

Strong doping of the n-optical confinement layer for increasing output power of high- power pulsed laser diodes in the eye safe wavelength range

An analytical model for internal optical losses at high power in a 1.5 μm laser diode with strong n-doping in the n-side of the optical confinement layer is created. The model includes intervalence band absorption by holes supplied by both current flow and two-photon absorption (TPA), as well as the direct TPA effect. The resulting losses are compared with those in an identical structure with a weakly doped waveguide, and shown to be substantially lower, resulting in a significant improvement in the output power and efficiency in the structure with a strongly doped waveguide.

Electronic Conductivity in a Porous Vanadyl Prussian Blue Analogue upon Air Exposure

Exposure to humid O2 or ambient air affords a 5-order-of-magnitude increase in electronic conductivity of a new Prussian blue analogue incorporating CoII and VIV-oxo units. Oxidation produces a mixed-valence framework, where the O2 exposure time controls the VIV/VV ratio and thereby the material's conductivity. The oxidized framework shows an intervalence charge-transfer band at ca. 4200 cm-1, consistent with mixed valence. The mixed-valence frameworks show semiconducting behavior with conductivity values of 10-5 S·cm-1 at room temperature and 10-4 S·cm-1 at 100 °C and activation energies of ca. 0.3 eV. N2 adsorption measurements at 77 K show that these materials possess permanent porosity before and after oxidation with Brunauer-Emmett-Teller surface areas of 340 and 370 m2·g-1, respectively.

On the infrared absorption coefficient measurement of thick heavily Zn doped GaAs using spectrally resolved modulated photothermal infrared radiometry

In this paper, we report on measurements of the infrared absorption coefficient in the mid-infrared range of a heavily Zn-doped GaAs wafer using spectrally resolved modulated photothermal infrared radiometry (PTR). The method allows us to measure the infrared absorption coefficient of (i) much thicker samples as compared to the one used in Fourier Transform Infrared (FTIR) spectroscopy in transmission configuration and (ii) with non-mirror-like surfaces as would be required for measurements in the reflection configuration. From the best fits of the theoretical model to the PTR results, the values of the infrared absorption coefficient and thermal diffusivity of GaAs wafer are obtained. These values of infrared absorption coefficients are compared both with the literature values on very thin, similarly doped GaAs:Be sample and with infrared absorption coefficients calculated from FTIR specular reflectance measurements on the same sample. FTIR reflectance measurements demand additional assumptions for the evaluation of absorption coefficient and mirror-like surfaces. The results obtained from both experimental methods yield the same order of the infrared absorption coefficients. It is observed that the infrared absorption coefficient decreases with increasing wavelength because of inter-valence band transitions. However, only the infrared spectrum estimated using PTR exhibits free carrier absorption effect at a shorter wavelength as observed in previous works on very thin Be-doped GaAs samples. It is worth mentioning that the presented method is not limited to semiconductors, but can be used for other highly infrared absorbing samples. In addition, the spectrally resolved PTR measurements simultaneously provide the same values of thermal diffusivity of the GaAs wafer within estimation uncertainties thus demonstrating the reliability of the PTR method in the measurement of thermal diffusivity of such samples.

Electrodeless measurement method of conduction type based on the free carrier absorption effect in CdZnTe

In this paper, we review theoretical and experimental studies on the infrared attenuation spectrum between 400 and 4000cm−1, which is principally due to the free carrier absorption (FCA). The free carrier absorption is possible by means of inter-conduction band transitions which occur in n-CdZnTe, or by means of inter-valence band transitions which occur in p-CdZnTe. Based on the power law fit results of absorption spectra determined by FCA characteristics, we present an optical measurement technique, which can help us to determine the conduction type of CdZnTe in another way.