Zn-doped InP Research Articles

Zinc Diffusion into InP via a Narrow Gap from a Planar Zn3P2-Based Source

An original technology of zinc diffusion into InP via a narrow gap is described, which allows reproducible formation of p–n junctions with preset depth of doping and retained surface morphology of the doped layers. Using the proposed method, desired charge carrier distribution profiles in Zn-doped InP layers were obtained. It has been experimentally confirmed that the method of cross-sectional scanning electron microscopy allows to precision measure of the zinc diffusion depth.

Photocurrent enhancement and magnetoresistance in indium phosphide single nanowire by zinc doping

We report the fabrication of intrinsic and Zn-doped InP single nanowire devices by the vapor–liquid–solid and photolithography techniques. Nanowires with a zincblend structure around 100 nm in radius and length at the micrometer scale were readily observed. Electrical measurements of samples containing single nanowires revealed Ohmic and Schottky behavior for the intrinsic and Zn-doped InP devices respectively. The Zn-doped InP device exhibited a thermal and optical dependence with high photosensitivity, whose main conduction mechanism for temperatures ranging from 160 K to 300 K was verified to be variable range hopping, displaying a hopping distance on the order of 240 nm at a low temperature. Strong temperature-dependent positive magnetoresistance was verified for this device.

Метод диффузии цинка в InP через узкий зазор с использованием планарного источника на основе Zn-=SUB=-3-=/SUB=-P-=SUB=-2-=/SUB=-

AbstractAn original technology of zinc diffusion into InP via a narrow gap is described, which allows reproducible formation of p–n junctions with preset depth of doping and retained surface morphology of the doped layers. Using the proposed method, desired charge carrier distribution profiles in Zn-doped InP layers were obtained. It has been experimentally confirmed that the method of cross-sectional scanning electron microscopy allows to precision measure of the zinc diffusion depth.

Increased Optoelectronic Quality and Uniformity of Hydrogenated p-InP Thin Films

The thin-film vapor–liquid–solid (TF-VLS) growth technique presents a promising route for high quality, scalable, and cost-effective InP thin films for optoelectronic devices. Toward this goal, careful optimization of material properties and device performance is of utmost interest. Here, we show that exposure of polycrystalline Zn-doped TF-VLS InP to a hydrogen plasma (in the following referred to as hydrogenation) results in improved optoelectronic quality as well as lateral optoelectronic uniformity. A combination of low temperature photoluminescence and transient photocurrent spectroscopy was used to analyze the energy position and relative density of defect states before and after hydrogenation. Notably, hydrogenation reduces the relative intragap defect density by 1 order of magnitude. As a metric to monitor lateral optoelectronic uniformity of polycrystalline TF-VLS InP, photoluminescence and electron beam induced current mapping reveal homogenization of the grain versus grain boundary upon hydroge...

Room-temperature electroluminescence from radial p–i–n InP/InAsP/InP nanowire heterostructures in the 1.5-µm-wavelength region

Crystal growth of radial p–i–n InP nanowires (NWs) with InAsP quantum well (QW) layers by metalorganic vapor-phase epitaxy was studied, and vertical NW light-emitting devices were fabricated. Radial p–i–n NWs were formed using position-controlled n-type InP NW cores. By optimizing the flow rates of the Zn source, Zn-doped p-type InP shells were grown on the sidewall of the radial QW structures while maintaining the photoluminescence intensity of the QWs. The fabricated devices showed current rectification originating from the p–i–n diode structures. Electroluminescence from the radial QWs was clearly observed in the 1.5-µm-wavelength region at room temperature for the first time.

Electronic properties of pure and p-type doped hexagonal sheets and zigzag nanoribbons of InP

Unlike graphene, a hexagonal InP sheet (HInPS) cannot be obtained by mechanical exfoliation from the native bulk InP, which crystallizes in the zinc blende structure under ambient conditions. However, by ab initio density functional theory calculations we found that a slightly buckled HInPS is stable both in pristine form and when doped with Zn atoms; the same occurred for hydrogen-passivated zigzag InP nanoribbons (ZInPNRs), quasi-one-dimensional versions of the quasi-two-dimensional material. We investigated the electronic properties of both nanostructures, in the latter case also in the presence of an external transverse electric field, and the results are compared with those of hypothetical planar HInPS and ZInPNRs. The band gaps of planar ZInPNRs were found to be tunable by the choice of strength of this field, and to show an asymmetric behavior under weak electric fields, by which the gap can either be increased or decreased depending on their direction; however, this effect is absent from slightly buckled ZInPNRs. The binding energies of the acceptor impurity states of Zn-doped HInPS and ZInPNRs were found to be similar and much larger than that of Zn-doped bulk InP. These latter findings show that the reduction of the dimensionality of these materials limits the presence of free carriers.

Electric field effect on the emission rate of H4F and H4S hole traps in InP

The electric field effect on the emission rate enhancement of the H4F and H4S hole trap in highly Zn-doped InP has been examined using the deep level transient spectroscopy (DLTS) and double correlation DLTS (DDLTS). The DLTS and DDLTS results have been found to be in good agreement for low and intermediate electric fields, but they disagree for large field effect. Comparing our emission data with the theory, we have found that H4F obeys the quantum model of phonon-assisted tunneling, while H4S follows the Poole–Frenkel model employing a three-dimensional screening Coulombic potential. Our results show that the H4S defect can be attributed to a charged (Vp–Zn) complex.

Investigation of negative electron affinity in hydrogen complex deactivated surface of InP:Zn (100)

Ultraviolet photoemission spectroscopy is used to investigate the development of negative electron affinity at the surface of hydrogenated Zn-doped InP (100). Hydrogen injected into the material electronically passivates the local carrier concentration. Reverse-biased anneals of the InP under ultrahigh vacuum show a dramatic change in the work function of the material within a set annealing temperature range suggesting the establishment of negative electron affinity at the surface. The strength of the negative electron affinity is 1.08eV. This value is consistent with the deactivation energy of the H–Zn complex (1.14eV) determined previously. Spectral features are also shown to be sensitive to sample temperature. Hydrogen retrapping at the surface limits the effect and it is dependent on whether the surface is smooth or roughened. The electron affinity of the material is thus controlled with defect density and annealing temperature.

Zn diffusion behavior at the InGaAsP/InP heterointerface grown using MOCVD

Zinc (Zn) diffusion through MOCVD-fabricated InP and InGaAsP layers, and the corresponding Zn doping profile at the heterojunction interface were studied as part of the doping profile control for laser diodes. It was found that the Zn doping profile has specific discontinuity at the heterojunction in InGaAsP/InP heterostructures. Using secondary ionization mass spectrometer (SIMS) and Boltzmann–Matano analysis for different composition ratios ( x) of (1− x)InP– xInGaAs epitaxial layers grown on Zn-doped InP substrates, it was found that the Zn diffusion coefficients were proportional to the square of the concentration in the InP and InGaAsP layers. The Zn diffusion coefficient strongly depends on the component ratio ( x) for the (1− x)InP– xInGaAs layer. It was concluded that this diffusion property is based on the higher stability of the substitutional Zn content in the InGaAs layer compared to that in the InP layer. The dependence of the Zn diffusion coefficient on Zn concentration in the InGaAsP/InP layers is explained based on the main diffusion source being Zn at the interstitial sites. The thermal equilibrium between Zn-interstitial and Zn-substitutional (interstitial–substitutional model) describes these Zn diffusion properties. Marked Zn concentrations at InGaAsP/InP heterojunctions are referred to as “pileups”, and are affirmed due to the difference in physical properties between InP and InGaAs. With different composition ratios ( x) of InP/InGaAsP layer growth, pre-control of the Zn concentration and strict limitations on the growth conditions before diffusion are indispensable for lasers requiring a precisely controlled doping concentration.

Five Simultaneously Q-Switch Mode-Locked Passive Laser Modulators

Five types of passive Q-switched as well as simultaneously Q-switch mode-locked modulators: plastic dye sheets (Kodak 9850 cellulose acetate dye sheets), lithium fluoride crystals containing F2 − color centers (LiF:F2 −), chromium-doped yttrium–aluminum–garnet crystals (Cr4+:YAG), ionic color filter glass (Schott RG1000 color filter glass), and the single crystal semiconductor wafers (GaAs, Fe-doped InP, Zn-doped InP, S-doped InP, etc.) used for modulation of the Nd:hosted(Nd:YAG, Nd:YVO4, and Nd:LSB) lasers were investigated in detail in our research. We also investigated applications of the Q-switch mode-locked pulse train for the development of a higher resolution solid-state laser range finder.

Diffusion of deuterium (hydrogen) in previously hydrogenated (deuterated) III–V semiconductors

Hydrogenated (deuterated) C-doped GaAs and Zn-doped InP layers have been exposed to a deuterium (hydrogen) plasma. Diffusion profiles have been measured by secondary ion mass spectroscopy and compared to those obtained after exposure of as-grown (without any previous plasma treatment) samples in identical plasma conditions. It is shown that a partial substitution of D (H) for H (D) occurs as a consequence of the breaking of the original H (D)–acceptor complexes. It is also demonstrated that, after the breaking, released H (D) species are trapped in the vicinity of the acceptor with which they were originally forming a complex.

Formation of vacancy-impurity complexes in heavily Zn-doped InP

Positron annihilation spectroscopy has been applied to observe the spontaneous formation of vacancy-type defects by annealing of heavily Zn-doped InP at 500--700 K. The defect is identified as the ${V}_{\mathrm{P}}\ensuremath{-}\mathrm{Zn}$ pair by detecting the annihilation of positrons with core electrons. We conclude that the defect is formed through a diffusion process; a phosphorus vacancy migrates until trapped by a Zn impurity and forms a negatively charged ${V}_{\mathrm{P}}\ensuremath{-}\mathrm{Zn}$ pair. The kinetics of the diffusion process is investigated by measuring the average positron lifetime as a function of annealing time and by fitting a diffusion model to the experimental results. We deduce a migration energy of $1.8\ifmmode\pm\else\textpm\fi{}0.2\mathrm{eV}\mathrm{}$ for the phosphorus vacancy. Our results explain both the presence of native ${V}_{\mathrm{P}}\ensuremath{-}\mathrm{Zn}$ pairs in Zn-doped InP and their disappearance in post-growth annealings.

Growth and characterization of Si, S and Zn-doped InP in selective area growth conditions

The incorporation and doping process of Si, S and Zn impurities in InP by metalorganic vapor phase epitaxy have been studied both in standard growth conditions (SGC) and in selective area growth (SAG) conditions using silane (SiH 4), hydrogen sulphide (H 2S) and diethylzinc (DEZn). It was observed that in SGC, the dopant species behaviour, for two different growth rates, is in line with the expectations from the model and some previous reports made on doped GaAs and InP. On the other hand, in SAG conditions, the Si concentration was unexpectedly independent of the growth rate. Furthermore, the Zn and S codoping shows a Zn dopant concentration enhancement in SAG conditions, while it remains constant in SGC. These differences in behaviour are induced by the addition of dopant species transported by lateral vapour phase diffusion from the patterned region to the open region.

The characteristics of Zn-doped InP using spin-on dopant as a diffusion source

Zn diffusion into InP was carried out ex-situ using a spin-on dopant as a diffusion source. The characteristics of Zn-doped InP are analyzed using low-temperature photoluminescence (PL), differential Hall measurement, and secondary ion mass spectrometry (SIMS). Dopant activation of Zn is close to 100% using this method. Band-to-acceptor (B-A) transition peak is dominant in PL, which is a characteristic usually found in in-situ doping. This evidence along with an activation energy of 0.5 eV show that the diffusion is substitutional rather than interstitial.

P-n Heterojunction Composed of n-ZnO/p-Zn-doped InP

A p-n junction was obtained by the deposition of an n-type ZnO thin film on a p-type Zn-doped InP substrate. The Zn-doped InP substrate has been made by the diffusion of Zn with sealed ampoule technique. The ZnO deposition process was performed by pulsed laser deposition (PLD). The p-n junction was formed and showed typical I-V characteristics. We will also discuss about the realization of an ultraviolet light-emitting diode (LED). The structure of n-ZnO/p-Zn-doped InP could be a good candidate for the realization of an ultraviolet light-emitting diode or an ultraviolet laser diode.

Formation Mechanism of Low Contact Resistance PdZn-based Ohmic Contacts for p-type InP

Recently, Sb(3 nm)/Zn(20 nm)/Pd(20 nm) ohmic contact materials to p-type InP which provides high reliable, low contact resistance after annealing at temperature around 375 ◦ C have been developed in our laboratories (where a slash (/) sign indicates the deposition sequence). The use of these contact materials for photodiodes made it possible to achieve simultaneous preparation of both p and n-type ohmic contacts, which resulted in significant reduction of the fabrication process steps. In the present paper in order to understand the mechanism of ohmic contact formation, the microstructural analysis of the interfaces between the Sb/Zn/Pd ohmic contacts and the Zn-doped p-type InP was carried out by X-ray diffraction, cross-sectional transmission electron microscopy, secondary ion mass spectroscopy, and electrochemical capacitancevoltage measurement. The present experiments proposed a new contact formation mechanism: reduction of the ohmic contact resistances was obtained primarily due to suppression of Zn (doped in the InP) outdiffusing from the InP substrate during annealing by the Pd 2InP layers which contained Zn. Thus the direct contact of the Pd2InP layers to the InP substrate was found to be essential to prevent reduction of the net acceptor concentration near the InP surface and also to improve the thermal stability of ohmic contacts. The roles of Pd and Sb added to the contact materials also contributed to the reduction of contact resistance and their roles will be discussed.

Mechanism of reverse current in the Al/p-InP schottky diodes

Reverse current-voltage characteristics of the Al/p-InP Schottky diodes based on Zn-doped InP epilayers were measured in relation to bias and temperature. Temperature dependence of reverse current is characterized by the activation energies of 0.75 and 0.51 eV in the high-temperature region and at temperatures T<280 K, respectively. Results are explained by the phonon-assisted tunneling generation of charge carriers from the surface states of a semiconductor with regard to the Frenkel emission mechanism. It is found that, in the low-temperature region, tunneling occurs via the centers with energy levels of 0.51 eV. Comparing experimental results with theory, we estimated electric-field strength in the barrier at (5–13)×107 V/m and the surface density of the hole charge in the boundary layer of the semiconductor.

Lasing from excited states in self-assembled InP/GaInP quantum islands

Aiming at laser emission in the visible part of the spectrum, we have investigated the growth of self-assembled InP quantum dots on GaInP by low-pressure metal-organic vapour phase epitaxy using the Stranski–Krastanow growth mode. These InP islands show a photoluminescence emission energy of 1.72 eV (90 K) at low excitation densities. Lasing was observed on optically pumped laser structures with a single layer of InP dots, GaInP waveguide material and AlInP cladding layers above an excitation density of 1.3 kW cm −2 at 90 K. The detected laser line is located at 1.8 eV, about 80 meV higher than the ground-state transition energy. We attribute this behaviour to lasing from excited states in agreement with power-dependent photoluminescence experiments and photoluminescence excitation measurements, and gain measurements using the variable stripe length method. These laser structures show stimulated emission under optical pumping up to room temperature above excitation densities of 30 kW cm −2. Furthermore, injection lasers with Si- and Zn-doped (Al 0.5Ga 0.5)InP cladding layers have been realised where lasing occurred above a threshold current density of 290 A cm −2 with an emission line at 1.78–1.82 eV (90 K).

Spectrally Resolved Cathodoluminescence Determination of Dopant Diffusion In InP/InGaAsP Based Multi Quantum Well Fabry-Perot Lasers

AbstractLow temperature monochromatic cathodoluminescence (CL) spectral analyses and imaging were used to determine the widths of resistive regions (due to Fe diffusion) in multi-quantum-well (MQW) InP-based laser devices and to detect the different amount of damage induced by alternative In-situ Etching (ISE) and Reactive Ion Etching (RIE) techniques. The widths of the resistive regions were estimated by comparing the 5 K CL emission width from the MQW and the actual width as obtained by SEM investigations. Monochromatic CL also did not reveal any emission from the InP:Sn layer between semi-insulating material (Fe-doped lnp) and p-type layer (Zn-doped InP), indicating interdiffusion of Fe and Zn laterally the MQW, and the presence of substantial Sn diffusion (up to 2500 nanometers) into the substrate.

Evidence for two distinct defects contributing to theH4deep-level transient spectroscopy peak in electron-irradiated InP

Deep-level transient spectroscopy (DLTS) has been used to study the dominant deep-level $H4$ produced in InP by electron irradiation. The characteristics of the $H4$ peak in Zn-doped InP has been studied as a function of pulse duration ${(t}_{p})$ before and after annealing. Our results show that at least two traps contribute to the $H4$ peak: one is a fast trap (labeled ${H4}_{F})$ and the other is a slow trap (labeled ${H4}_{S}).$ This is shown through several results concerning the activation energy, the capture cross section, the full width at half-maximum, and the peak temperature shift. It is shown that both traps are irradiation defects created in the P sublattice.