Binary InP Research Articles

Systematic Assessment of Phonon and Optical Characteristics for Gas-Source Molecular Beam Epitaxy-Grown InP1−xSbx/n-InAs Epifilms

Experimental and theoretical assessments of phonon and optical characteristics are methodically accomplished for comprehending the vibrational, structural, and electronic behavior of InP1−xSbx/n-InAs samples grown by Gas-Source Molecular Beam Epitaxy. While the polarization-dependent Raman scattering measurements revealed InP-like doublet covering optical modes (ωLOInP~350 cm−1, ωTOInP~304 cm−1) and phonons activated by disorders and impurities, a single unresolved InSb-like broadband is detected near ~195 cm−1. In InP1−xSbx, although no local vibrational (InSb:P; x → 1) and gap modes (InP:Sb; x → 0) are observed, the Raman line shapes exhibited large separation between the optical phonons of its binary counterparts, showing features similar to the phonon density of states, confirming “two-mode-behavior”. Despite the earlier suggestions of large miscibility gaps in InP1−xSbx epilayers for x between 0.02 and 0.97, our photoluminescence (PL) results of energy gaps insinuated achieving high-quality single-phase epilayers with x ~ 0.3 in the miscibility gap. Complete sets of model dielectric functions (MDFs) are obtained for simulating the optical constants of binary InP, InSb, and ternary InP1−xSbx alloys in the photon energy (0 ≤ E ≤ 6 eV) region. Detailed MDF analyses of refractive indices, extinction coefficients, absorption and reflectance spectra have exhibited results in good agreement with the spectroscopic ellipsometry data. For InP0.67Sb0.33 alloy, our calculated lowest energy bandgap E0 ~ 0.46 eV has validated the existing first-principles calculation and PL data. We feel that our results on Raman scattering, PL measurements, and simulations of optical constants provide valuable information for the vibrational and optical traits of InP1−xSbx/n-InAs epilayers and can be extended to many other technologically important materials.

InAsP/AlGaInP/GaAs QD laser operating at ∼770 nm

We present a study of metalorganic vapour phase epitaxy of ternary InAsP quantum dots in AlGaInP/GaAs for application in laser diodes. The properties of InAsP QD laser structures were compared with reference samples containing binary InP QDs. Based on X-ray diffraction, the molar fraction of arsenic in InAsP QDs was estimated to be ∼25%. Room temperature liquid contact electro-luminescence measurements revealed a long wavelength shift of the InAsP QD emission to ∼775 nm as compared with the InP QD emission at 716 nm and an increased full width at half maximum of the spontaneous emission (71 meV vs 50 meV). As cleaved, 4 mm long and 50 pm wide InAsP QD lasers operated in a pulsed regime at room temperature at ∼770 nm with a threshold current density of 155 A/cm2 and a maximum output optical power of at least 200 mW. The maximum operation temperature was at least 380 K.

Core and surface engineering in binary, ternary and quaternary semiconductor nanocrystals—A critical review

In the past two decades significant research efforts of chemists, physicists, materials scientists and electronic engineers have been devoted to the elaboration of semiconductor nanocrystals with controlled optoelectronic properties and dispersable in various media, including aqueous ones. This review discusses problems of the inorganic nanocrystals synthesis with special emphasis on the role of initial ligands i.e. ligands originating from the reaction mixture in this process. Chemical nature of initial ligands and their topology have a profound effect on the nanocrystals’ shape and size, as well as on their physical properties. Also methods for identification of initial ligands are outlined. Classification of these ligands is presented and their interactions with nanocrystal surface is discussed in the frame of HSAB (hard and soft (Lewis) acid and bases) theory. Since exchange of initial ligands for functional ones, which could tune electrical transport and other properties of the resulting nanomaterials, is crucial for nanocrystals engineering, effective ligands exchange procedures are also described, including exchange for organic ligands of semiconductor nature. Not neglecting initially developed nanocrystals (CdSe and PbS), frequently considered as “model” systems, in this review special interest is focused on heavy metal-free nanocrystals, attracting increasing scientific interests in recent years, namely binary InP NCs, ternary stoichiometric (CuInS2) and nonstoichiometric (Cu-In-S) NCs, and quaternary Cu-In-Zn-S ones. To enhance practical utility of this review, recommended nanocrystals preparation methods, resulting in different initial ligands, as well as ligands exchange procedures are presented for each group of the discussed nanocrystals.

Type-II InP/GaAsSb double-heterojunction bipolar transistors with fMAX > 700 GHz

The “type-II” staggered band lineup at the base-collector junction of InP/GaAsSb double-heterojunction bipolar transistors (DHBTs) eliminates the current blocking effect observed in InP/GaInAs DHBTs and allows the use of a pure binary InP collector that provides a high breakdown voltage and good thermal conductivity. Improvement of the power gain cutoff frequency fMAX requires a reduction in base resistance and/or base-collector capacitance. We have decreased the base contact resistivity by in situ Ar sputtering immediately prior to the base contact deposition. The resulting DHBTs simultaneously feature fT = 429 GHz and fMAX = 715 GHz. To the best of the authors’ knowledge, this is the highest reported fMAX for InP/GaAsSb-based DHBTs to date.

Native point defects in binary InP semiconductors

We present a holistic method to identify stable point defects in InP and the position of their defect states within the experimental band gap using density functional theory. We have calculated the formation energy of the different charge neutral native point defects for both stoichiometric and non-stoichiometric InP by determining the chemical potentials of In and P within the compound correctly from thermodynamic considerations. For stoichiometric InP, we predict phosphorous vacancies and phosphorus antisites to be most probable, among the neutral defects. For In-rich and P-rich compositions, we find indium and phosphorous antisites to be most stable, respectively, when neglecting charges. We then present a careful analysis to identify the defect levels associated with each point defect within the experimental band gap and compare it with existing experiments. By comparing calculations with different cell sizes and with varying band gaps from different exchange–correlation functionals (GGA vs. hybrid functional), we examine the dependence of the defect states on cell size and position of the excited states and analyze their nature and expected position in real systems along with the resulting charges on the defects. Finally, we include a recipe to approximate the Fermi level dependence of the chemical potential of charged defects in binary compounds, allowing calculation of their formation energies. Considering charges, the dominant point defects for stoichiometric InP are +4 and +2 charged indium and phosphorous antisites for Fermi energies 1.1 eV, respectively. For non-stoichiometric InP, the respective antisites are constitutional defects in their minimum-energy charge states, depending on the Fermi level.

High-Current-Gain InP/GaInP/GaAsSb/InP DHBTs With $f_{T} = \hbox{436}\ \hbox{GHz}$

Combining a pseudomorphically strained (Ga,In)P emitter with a GaAs0.6Sb0.4 base effectively eliminates the emitter heterojunction type-II conduction band offset in InP/GaAsSb double heterojunction bipolar transistors (DHBTs). A peak fT of 436 GHz at JC = 10 mA/mum2, with BVCEO = 3.8 V, is achieved with 0.6 times 5 mum2 InP/GalnP/GaAsSb DHBTs with a 75-nm InP collector. Compared to a binary InP emitter, the (Ga,In)P emitter doubles the DC current gain from 166 to 338 for otherwise identical devices. These are the highest DC current gain and cutoff frequencies to date in uniform base GaAsSb DHBTs. The gain improvement reported here will greatly facilitate device design tradeoffs that are encountered while scaling InP/GaAsSb DHBTs toward higher frequencies by allowing higher base doping levels and smaller emitter geometries.

Unified explanation for suppressed electron ionization coefficient and its weak temperature dependence in InGaP

Experimental evidence of electron multiplication, extracted from InGaP–GaAs–InGaP double heterojunction bipolar transistors, reveals a suppressed electron impact ionization coefficient, αn, with weak temperature dependence in InGaP compared to those measured from binary InP and GaP, which could not be predicted by the widely used Okuto–Crowell relation assuming that the optical phonon scattering is the only dominant scattering process during impact ionization. We show that discrepancies between the experimental data and the Okuto–Crowell relation can be consistently ascribed to the involvement of alloy scattering. This provides an improved insight into understanding the presence of alloy scattering on carrier impact ionization behavior in InGaP.

Growth of ternary InAlP and InGaP self-assembled quantum dots by metalorganic chemical vapor deposition

We report the characteristics of ternary InAlP and InGaP self-assembled quantum dots grown by metalorganic chemical vapor deposition. The structural and optical properties of these ternary quantum dots are compared with the characteristics of binary InP quantum dots grown under similar conditions. Because these ternary quantum dots have different bandgaps, strain, and composition compared to binary InP quantum dots, the ternary quantum-dot optical and physical properties are markedly different. The quantum-dot structures are grown uncapped (exposed QDs) and capped (embedded QDs) and characterized by atomic force microscopy (AFM) and photoluminescence (PL). InAlP quantum dots have higher densities and smaller sizes and InGaP quantum dots have smaller densities, as compared with InP quantum dots grown under similar conditions. Also, a random and broad size distribution is observed for InGaP quantum dots and the luminescence from InGaP dots is broader than for InP quantum dots.

Noise performance of InGaAs-InP quantum-well infrared photodetectors

Dark current noise measurements were carried out between 10 and 10/sup 4/ Hz at T=80 K on two InGaAs-InP quantum-well infrared photodetectors (QWIPs) designed for 8-/spl mu/m infrared (IR) detection. Using the measured noise data, we have calculated the thermal generation rate, bias-dependant gain, electron trapping probability, and electron diffusion length. The calculated thermal generation rate (/spl sim/7/spl times/10/sup 22/ cm/sup -3//spl middot/s/sup -1/) is similar to AlGaAs-GaAs QWIPs with similar peak wavelengths, but the gain is 50/spl times/ larger, indicating improved transport and carrier lifetime are obtained in the binary InP barriers.

Lpe growth method possibilities in A3B5 semiconductors preparation

Pre-diffusion limited technique of liquid phase epitaxy is used for preparation of quaternary solid solution GaxIn1−xAsyP1−y and binary InP. Surface morphology of the layers prepared at this condition has been compared with those prepared by conventional LPE. Quaternary strained layers with composition near to Ga0.21In0.79As0.75P0.25 were grown with perpendicular lattice mismatch up to 1.6% in compression, on the InP substrates of (100) orientation. The used epitaxial technique has been modified for perspective attempt to heal the growth interfaces. Modification was tested by InP growth.

Raman scattering of slab-mode phonons in InGaAsP/InP multiple quantum wells

Raman light scattering experiments in lattice-matched InGaAsP/InP multiple quantum wells are reported. Use of laser light below the InP band gap permitted study of right-angle scattering with the scattered light emerging parallel to the layers. Scattering by the binary InP longitudinal optic (LO) and transverse optic (TO) phonons dominated the spectra. The polarization selection rules for the TO and LO scattering were found to differ strongly compared to those operative in bulk InP. This is interpreted as arising from the interchange of the LO and TO phonon frequencies as expected in a dielectric continuum slab whose thickness is small compared to the wavelength of the incident radiation. In addition weak Raman scattering by a mixture of InGaAs and InP vibrations in the quaternary well material is reported.

Kinetic study of metalorganic molecular beam epitaxy of GaP, InP, and GaxIn1−xP

The growth rates of GaP and InP deposited by metalorganic molecular beam epitaxy using triethylgallium, trimethylindium, and precracked phosphine have been studied by reflection high energy electron diffraction and related to composition variations of the ternary alloy GaxIn1−xP. The influence of the substrate temperature and phosphine flow rate have been investigated for each material. The GaP growth rate dependence with temperature exhibits qualitatively the same behavior as already reported for the growth of GaAs by metalorganic molecular beam epitaxy. In the case of InP, a constant growth rate is observed in the temperature range of 450–500 °C. At higher temperatures, a strong decrease of the growth rate, attributed to the desorption of dimethylindium species, is measured. Meanwhile, the GaxIn1−xP composition is found to become Ga rich while increasing temperature. Furthermore, it is found to significantly depend on the phosphine flow rate at a fixed temperature. In the low phosphine flow regime, the composition is associated with the preferential formation of GaP bonds, and in the high phosphine flow regime, the composition is closely correlated with the sharp decrease observed for the binary InP growth rate.

Effective mass of holes in quaternary InGaAsP alloys lattice-matched to InP

Abstract Rapid growth of optical communications technology over the last decade is largely due to the development of InGaAsP/InP light sources and detectors whose operating wavelengths match the low-loss and low-dispersion windows of silica fibers. Proper design of such devices is, to a large extent, conditional upon the detailed knowledge of relevant material characteristics. In spite of intensive studies of InGaAsP quaternary alloy semiconductors prompted by their practical applications,1–4 there remain a number of important parameters for which only rough estimates are available. Such is the case of the heavy-hole effective mass, which is one of the least-known parameters even in the case of the binary InP.