Mg-doped GaAs Research Articles

Mg-Doped GaAs Nanowires with Enhanced Surface Alloying for Use as Ohmic Contacts in Nanoelectronic Devices

In this work, we have investigated the structural and electronic properties of Mg-doped GaAs(111) nanowires synthesized through a vapor–liquid–solid growth mechanism. The crystalline structure of these nanowires was measured using synchrotron X-ray diffraction, while their electronic structure was addressed by scanning tunneling spectroscopy. Scanning tunneling microscopy measurements revealed that conducting Ga2Mg/Mg clusters are observed at {110} nanowire lateral surfaces, allowing electrical contacts with reduced Schottky barriers. This suggests that similar alloyed surfaces can be produced with other dopants, enabling the development of distinct Ohmic contacts in these systems. Density functional theory was used to investigate the electronic response of Ga2Mg. While at room temperature, electronic variable-range hopping drives the nanowires into a metallic behavior, quantum confinement is observed at low temperatures.

Optical and Surface Characteristics of Mg-Doped GaAs Nanocrystalline Thin Film Deposited by Thermionic Vacuum Arc Technique

Magnesium (Mg) is the most promising p-type dopant for gallium arsenide (GaAs) semiconductor technology. Mg-doped GaAs nanocrystalline thin film has been deposited at room temperature by the thermionic vacuum arc technique, a rapid deposition method for production of doped GaAs material. The microstructure and surface and optical properties of the deposited sample were investigated by x-ray diffraction analysis, scanning electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, ultraviolet–visible spectrophotometry, and interferometry. The crystalline direction of the deposited sample was determined to be (220) plane and (331) plane at 44.53° and 72.30°, respectively. The Mg-doped GaAs nanocrystalline sample showed high transmittance.

GaInP/GaAs tandem solar cells with highly Te- and Mg-doped GaAs tunnel junctions grown by MBE**Project supported by the SINANO-SONY Joint Program (Grant No. Y1AAQ11001), the National Natural Science Foundation of China (Grant No. 61274134), the USCB Start-up Program (Grant No. 06105033), and the International Cooperation Projects of Suzhou City, China (Grant No. SH201215).

We report a GaInP/GaAs tandem solar cell with a novel GaAs tunnel junction (TJ) with using tellurium (Te) and magnesium (Mg) as n- and p-type dopants via dual-filament low temperature effusion cells grown by molecular beam epitaxy (MBE) at low temperature. The test Te/Mg-doped GaAs TJ shows a peak current density of 21 A/cm2. The tandem solar cell by the Te/Mg TJ shows a short-circuit current density of 12 mA/cm2, but a low open-circuit voltage range of 1.4 V∼1.71 V under AM1.5 illumination. The secondary ion mass spectroscopy (SIMS) analysis reveals that the Te doping is unexpectedly high and its doping profile extends to the Mg doping region, thus possibly resulting in a less abrupt junction with no tunneling carriers effectively. Furthermore, the tunneling interface shifts from the intended GaAs n++/p++ junction to the AlGaInP/GaAs junction with a higher bandgap AlGaInP tunneling layers, thereby reducing the tunneling peak. The Te concentration of ∼ 2.5 × 1020 in GaAs could cause a lattice strain of 10−3 in magnitude and thus a surface roughening, which also negatively influences the subsequent growth of the top subcell and the GaAs contacting layers. The doping features of Te and Mg are discussed to understand the photovoltaic response of the studied tandem cell.

New insights into the temperature-dependent photoluminescence of Mg-doped GaAs nanowires and epilayers

The intentional introduction of impurities in semiconductor nanowires is very important in view of device applications. Doping affects the electronic energy level structure which in the case of III–V nanowires can also be strongly influenced by the simultaneous occurrence of two polytypes, zinc-blende (ZB) and wurtzite (WZ). In this work, we report a study on GaAs nanowires with different Mg-acceptor doping levels through temperature dependent photoluminescence. A comparable investigation is presented for Mg-doped GaAs epilayers. For the later, only a band is observed which is ascribed to the involvement of the Mg acceptor due to the observed bandgap energy narrowing effect with increasing the doping level, and the temperature dependent behaviour. A different behaviour is reported for nanowires: several radiative transitions are observed whose temperature dependence follows that of bulk GaAs, in accordance with spatially indirect recombination. Although the polytypic regions mask the role of doping in nanowires it favours the charge separation required for photovoltaic applications.

GaAs tunnel junction grown using tellurium and magnesium as dopants by solid-state molecular beam epitaxy

We report a GaAs tunnel junction grown by all-solid-state molecular beam epitaxy (MBE), using tellurium (Te) and magnesium (Mg) as n- and p-type dopants, respectively. The growth conditions, including V/III ratio, and growth rate, growth temperature, were optimized. Through these optimizations, Te- and Mg-doped GaAs with high carrier concentrations as well as good mobilities were obtained. A GaAs tunnel junction with a peak current density of 21 A/cm2 was demonstrated.

Structural and optical characterization of Mg-doped GaAs nanowires grown on GaAs and Si substrates

We report an investigation on the morphological, structural, and optical properties of large size wurtzite GaAs nanowires, low doped with Mg, grown on GaAs(111)B and Si(111) substrates. A higher density of vertical nanowires was observed when grown upon GaAs(111)B. Very thin zinc-blende segments are observed along the axis of the nanowires with a slightly higher linear density being found on the nanowires grown on Si(111). Low temperature cathodoluminescence and photoluminescence measurements reveal an emission in the range 1.40–1.52 eV related with the spatial localization of the charge carriers at the interfaces of the two crystalline phases. Mg related emission is evidenced by cathodoluminescence performed on the GaAs epilayer. However, no direct evidence for a Mg related emission is found for the nanowires. The excitation power dependency on both peak energy and intensity of the photoluminescence gives a clear evidence for the type II nature of the radiative transitions. From the temperature dependence on the photoluminescence intensity, non-radiative de-excitation channels with different activation energies were found. The fact that the estimated energies for the escape of the electron are higher in the nanowires grown on Si(111) suggests the presence of wider zinc-blende segments.

Photoluminescence study of GaAs thin films and nanowires grown on Si(111)

Mg-doped GaAs nanowires have been grown by molecular beam epitaxy on a partially Au-coated Si(111) substrate by the vapor–liquid–solid mechanism. Outside the coated areas, a thin film of GaAs was grown epitaxially at the same time. The optical properties in both parts of the sample were investigated by photoluminescence spectroscopy, as a function of temperature. A structured emission in the range ∼1.25–1.55 eV was observed at 10 K and the resemblances in both cases were identified. The radiative transitions are discussed with relevance to known defect centers in the GaAs thin films and to their possible relation with the zinc-blende and wurtzite phases in the nanowires. The presence of both crystalline phases in the nanowires was confirmed by μ-Raman spectroscopy.

Growth and optical characteristics of Mg-doped GaAs epitaxial layers by molecular beam epitaxy

Photoluminescence (PL) measurement is used to study the optical properties of Mg-doped GaAs epitaxial layers grown by molecular beam epitaxy (MBE) with various growth temperatures. Four dominant PL peaks are observed, which may be associated with free-to-bound (e–A), exciton-bound to neutral acceptor (A oX), and two kinds of acceptor associated (g, g–g) transitions. The g and g–g peaks are especially prominent in a sample with a carrier concentration of 2.3 × 10 17 cm −3. To investigate the behavior of each peak as a function of temperature, PL measurements were carried out over a temperature range of 18–152 K. The A oX peak position follows the Varshni model for GaAs with increasing temperature. For the g and A oX peaks, we observe an increase in PL intensity with increasing temperature from 18 to 28 K. This phenomenon is known as “negative thermal quenching (NTQ)”, and it is observed in the g peak for the first time in this paper.

Electrical characteristics of Mg-doped GaAs epitaxial layers grown by molecular beam epitaxy

The electrical characteristics of magnesium (Mg)-doped GaAs epitaxial layers grown with different substrate temperatures have been investigated by Hall effect and capacitance–voltage (C–V) measurements at room temperature. The carrier concentration obtained by Hall measurements was decreased from 1.4×1019 to 3.4×1016 cm−3 when increasing the substrate temperature in the range 460–540 °C, and thus the maximum attainable doping density was NA–ND=1.4×1019 cm−3. The depth profiles of doping density, obtained by C–V measurements, show that carriers largely out-diffused toward the surface. This could be attributed to the surface segregation effect, which was predominant in the samples with a high doping density than those with a low doping density. Mg-doped GaAs layers have higher mobility than Be-doped GaAs layers around NA–ND=1018 cm−3. Thus, it is expected that Mg could be effectively used as p-type dopants for highly doped nanostructured semiconductors.

A study on maskless selective growth of Mg-doping p-type GaAs using low-energy focused ion beam

Maskless selective growth of Mg-doped GaAs films was performed by using a low-energy (30–200 eV) Mg–Ga focused ion beam (FIB) under the ambient of As 4 molecular beam. Under suitable As 4 pressure, all samples showed p-type and the carrier concentrations were around 10 17 cm −3. We achieved very high sticking coefficient of Mg ( k Mg of nearly 10 −1) compared with the result obtained at Molecular beam epitaxy (MBE) growth ( k Mg of nearly 10 −5). A p–n junction was formed on n +-type GaAs substrate by maskless selective growth. The diode showed typical I– V characteristics and the quality factor ( n-value) was approximately 1.75 for the sample grown at 60 eV. These results indicate that this method would be suitable for making maskless selective micro-device fabrication.

High-power and high-temperature operation of Mg-doped AlGaInP-based red laser diodes

This paper reports on high-power and high-temperature operation of an AlGaInP-based high-power red laser diode with magnesium (Mg)-doped quaternary-alloy cladding layer. The use of Mg dopant with small diffusion coefficient enables abrupt doping profiles as well as high carrier concentrations when compared to conventional zinc (Zn) dopant. It was also found that the metal-organic vapor phase epitaxial (MOVPE) growth of Mg-doped quaternary AlGaInP alloy is not affected by so-called reactor memory effects, while unintentional incorporation of Mg is observed in GaAs after the growth of Mg-doped GaAs layers. The higher carrier concentration in the p-type cladding layer enhanced carrier confinement in the active layer so that device performance at high temperature is improved. The abrupt doping profile suppressing dopant diffusion into the active layer eliminates the nonradiative recombination in the active layer resulting in higher external quantum efficiency. The characteristic temperature of the Mg-doped red laser with a lasing wavelength of 659 nm is as high as 167 K while the Zn-doped laser exhibits a temperature of 127 K. High kink-free output power of 150 mW is achieved at 75/spl deg/C.

Growth of High Quality Mg-doped GaAs by molecular Beam Epitaxy and Its properties

Jong Su Kim, D. Y. Lee, I. H. Bae, J. I. Lee, S. K. Noh, Jin Soo Kim, Gu Hyun Kim, Seungil Ban, Se-Kyung Kang, S. M. Kim, J. Y. Leem, M. Jeon, J. S. Son. J. Korean Phys. Soc. 2001;39:S518-. https://doi.org/10.3938/jkps.39.S518

Passivation and thermal reactivation of Mg acceptors inp-type GaAs

This paper reports on the efficient passivation of Mg-doped GaAs. The extent of the passivation was demonstrated to be highly temperature dependent, with the passivation being even more efficient than that of Zn-doped GaAs at temperatures below $140\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ By performing reverse bias annealing measurements between 60 and $130\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ we observed the reactivation of the Mg acceptors within the high-field region of the Schottky diode. This reactivation was found to obey first-order kinetics, with a dissociation energy ${E}_{\mathrm{MgH}}=(0.90\ifmmode\pm\else\textpm\fi{}0.03) \mathrm{eV}$ and an attempt frequency ${\ensuremath{\nu}}_{0}{=(3}_{\ensuremath{-}2}^{+5})\ifmmode\times\else\texttimes\fi{}{10}^{8} {\mathrm{s}}^{\ensuremath{-}1}.$ These results suggest that the Mg-H configuration is not bond centered, as also suggested by previous infrared absorption studies.

Carbon diffusion in undoped, n-type, and p-type GaAs

The effects of background doping, surface encapsulation, and As4 overpressure on carbon diffusion have been studied by annealing samples with 1000 Å p-type carbon doping spikes grown within 1 μm layers of undoped (n−), Se-doped (n+), and Mg-doped (p+) GaAs. The layers were grown by low-pressure metalorganic chemical vapor deposition using CCl4 as the carbon doping source. Two different As4 overpressure conditions were investigated: (1) the equilibrium pAs4 over GaAs (no excess As), and (2) pAs4 ∼2.5 atm. For each As4 overpressure condition, both capless and Si3N4-capped samples of the n−-, n+-, and p+-GaAs crystals were annealed simultaneously (825 °C, 24 h). Secondary-ion mass spectroscopy was used to measure the atomic carbon depth profiles. The carbon diffusion coefficient is always low, but depends on the background doping, being highest in Mg-doped (p+) GaAs and lowest in Se-doped (n+) GaAs. The influence of surface encapsulation (Si3N4) and pAs4 on carbon diffusion is minimal.

Electrical and optical properties of heavily doped Mg- and Te-GaAs grown by liquid-phase epitaxy

GaAs epitaxial layers doped with Mg and Te were grown on (100) GaAs substrates by liquid-phase epitaxy with a 6°C supersaturation temperature. Room-temperature carrier concentrations up to 2 × 10 19 cm −3 for p-type and 2.6 × 10 19 cm −3 for n-type dopants were obtained reproducibly. Carrier mobilities at 77 K in both n- and p-type layers showed a sharp drop at concentrations higher than 2 × 10 19 cm −3. The full width at half maximum value and the relative intensity of the photoluminescent spectrum increased and decreased, respectively, with carrier concentrations for both Mg- and Te-doped layers, and showed abrupt slope variations near a carrier concentration of 1 × 10 19 cm −3. In Mg-doped GaAs layers, the peak wavelength of photoluminescence spectra increased with hole concentration due to band-gap shrinkage. On the other hand, the photoluminescence peak wavelength decreased with electron concentration due to a Burstein-Moss shift and to band-tailing effects in the Te-doped GaAs layers.

Liquid-phase epitaxy of heavily Mg-doped GaAs: Formation of a new near-band-edge emission exclusively pertinent to acceptor impurities

Liquid-phase epitaxy (LPE) of Mg-doped GaAs was carried out. An extremely heavy doping was accomplished with a maximum net hole concentration of 1.31×1019 cm−3. A systematic investigation of photoluminescence spectra was performed as a function of hole concentration, which revealed that a newly discovered emission characterizing acceptor impurities can be obviously recognized also in LPE-grown samples in spite of the fact that the selective optical compensation effect among doped acceptors and residual donors presumably coming from Si of the LPE quartz tube is supposed to be comparatively strong. The red shift of this emission energy with increasing hole concentration and its locking at high hole concentration were discussed theoretically by introducing a preliminary model, i.e., a pair between excited-state acceptors.

A theoretical explanation for the red energy shift of a newly discovered, exclusively acceptor-associated emission in GaAs

Radiative mechanism of a newly discovered near-band-edge emission, [g-g], exclusively associated with acceptor impurities in GaAs, was theoretically discussed. Since the emission energy of [g-g] for the lowest acceptor concentration limit is nearly identical to that of the excited state of the acceptor impurities and it shows a noticeable shift towards lower-energy levels with increasing acceptor concentration, it was suggested that the energy of [g-g] corresponds to the 2pσ bond state of the acceptor-acceptor pair formed by the overlapping of the 2p excited state. The calculated energy of the 2pσ bond as a function of the distance between the acceptor-acceptor pair shows good agreement with the experimentally obtained value of [g-g] in Mg-doped GaAs grown by molecular-beam epitaxy (MBE). From a comparison of binding energies in the acceptor-doped GaAs samples prepared by ion implantation (Zn+ or Mg+) and by MBE, the activation ratio of the implanted atoms was estimated.

Photoluminescence of Mg-doped GaAs grown by molecular beam epitaxy using Mg3As2 as a Mg source: A comparison with Mg+ ion implantation

Photoluminescence spectra of Mg-doped GaAs grown by molecular beam epitaxy (MBE) are for the first time reported. Mg was introduced during MBE growth by using a synergic reaction of Mg3As2. Two near-band-edge emissions, g and [g-g], were observed below bound exciton emissions which were originally obtained in Mg+ ion-implanted GaAs. It is explicitly demonstrated that there is no essential difference of photoluminescence spectra between Mg+ ion-implanted GaAs and the present material. These results conclusively indicate that the above two emissions are definitively related with the acceptor levels and exclusively not associated with crystalline defects produced by ion implantation. It is additionally presented that [g-g] is principally established also in Mg-doped GaAs prepared by liquid phase epitaxy, where [g-g] is significantly suppressed due to the unintentional incorporation of Si donor atoms. For moderately Mg-doped GaAs prepared by MBE a new fine emission with a doublet structure, temporarily denoted by AX, is obtained 5 meV below (A0, X) a bound exciton emission at neutral acceptors.

An alternative Mg precursor for p-type doping of OMVPE grown material

A new Mg precursor, bis(methylcyclopentadienyl)magnesium has been studied. This source, used as a liquid, produced hole concentrations of 5×10 19 to 2×10 19 cm ×3 in GaAs. Surface morphologies in this doping range for GaAs layers are excellent. Electrical and optical evaluations indicate low compensation and material comparable to Mg-doped GaAs using other precursors. Some dopant tailing has been observed.

OM-VPE growth of Mg-doped GaAs

The epitaxial growth of Mg-doped GaAs by the organometallic vapour phase epitaxial process (OM-VPE) has been achieved for the first time. The doping is controllable over a wide range of input fluxes of bis (cyclopentadienyl) magnesium, (C5H5)2Mg, the organometallic precursor to Mg.