P-type Carrier Concentration Research Articles

Investigation of the indium-boron interaction in silicon

The interaction between indium and boron coimplanted in silicon has been investigated. In particular, the effects of the coimplantation on the diffusion and the electrical activation have been studied in comparison with the single B or In implanted samples. It is shown that, by means of coimplantation, it is possible to obtain p-type carrier concentration profiles with a concentration peak higher than the ones achievable by the single In doping, but with the further advantage of a shallower carrier distribution with respect to the single B implant. It is found that this is due to the formation of In–B complexes with an acceptor level deeper than the one related to substitutional B.

Characterization of SnTe films grown by molecular beam epitaxy

A series of SnTe layers with thicknesses varying from 0.42 to 9.1 µm were grown by molecular beam epitaxy on (111) BaF2 substrates. The SnTe lattice parameter was found to be 6.331 Å as determined from x-ray diffraction spectra measured in the triple-axis configuration. The FWHM of the (222) SnTe x-ray rocking curves indicated a good crystalline quality and an unusual dependence on layer thickness. Atomic force microscopy (AFM) of the SnTe surface revealed spirals with monolayer steps formed around threading dislocations, similar to the PbTe on BaF2 epitaxy. The dislocation density was estimated from the AFM picture to be 9x10(8) cm-2. Small black pits corresponding to holes that were left during growth were also observed on the AFM images. Sn diffusion can be a possible reason for these pits and the relatively high dislocation density. Electrical measurements showed that the SnTe epilayers present a typical p-type carrier concentration around 10(20) cm- 3 almost temperature independent and a Hall mobility which decreases from 10(4) to 10³ cm²/V.s as the temperature increases from 10 to 350K.

Growth and properties of magnetron cosputtering grown Mn xGe 1− x on Si (001)

We have grown Mn x Ge 1− x films ( x=0, 0.06, 0.1) on Si (001) substrates by magnetron cosputtering, and have explored the resulting structural, morphological, electrical and magnetic properties. X-ray diffraction results show there is no secondary phase except Ge in the Mn 0.06Ge 0.94 film while new phase appears in the Mn 0.1Ge 0.9 film. Nanocrystals are formed in the Mn 0.06Ge 0.94 film, determined by field-emission scanning electron microscopy. Hall measurement indicates that the Mn 0.06Ge 0.94 film is p-type semiconductor and hole carrier concentration is 6.07×10 19 cm −3 while the Mn x Ge 1− x films with x=0 has n-type carriers. The field dependence of magnetization was measured using alternating gradient magnetometer, and it has been indicated that the Mn 0.06Ge 0.94 film is ferromagnetic at room temperature.

Electronic properties of polycrystalline LaFeO 3. Part II: Defect modelling including Schottky defects

The electrical conductivity of polycrystalline LaFeO 3 is reported as a function of temperature. The conductivity of LaFeO 3 was shown to be affected by annealing for extended periods (about one week) at temperatures above 1000 °C prior to the conductivity measurements. Higher annealing temperatures resulted in higher conductivity. This effect was explained by the formation of Schottky cation defects, which act as electron acceptors, leading to an increasing conductivity with increasing annealing temperature. Below 1000 °C, the conductivity was unaffected by the annealing temperature, probably due to the low mobility of cation vacancies. A model for the defect chemistry and conductivity of LaFeO 3, including the formation of Schottky defects is proposed. The model reproduces quantitatively the dependence of the conductivity with respect to the partial pressure of oxygen at 1000 °C. The electronic mobilities of the charge carriers in the material were determined by the conductivity of La 0.99Sr 0.01FeO 3, where the charge carrier concentration is given by the dopant level. The model also predicts that the concentration of p-type charge carriers in air is increasing with temperature due to the formation of Schottky defects, for a limited temperature interval above 1000 °C.

Growth and Characterization of InGaNAs Quaternary Alloys for the Fabrication of Long Wavelength MSM Photodetectors on GaAs Substrates

ABSTRACTIn this paper, the optical and electrical properties of both as-grown and annealed thick InxGa1−xNyAs1−y layers grown by metal organic chemical vapour deposition (MOCVD) are presented. Through careful control of the trimetylyindium (TMIn), dimetylyhydrazine (DMHy), trimethylgallium (TMGa) and arsine (AsH3) precursors, lattice matching conditions were achieved for epitaxial layers containing up to 3% nitrogen (0≤y≤0.03) and 11% indium (0≤x≤0.11) with bandgap wavelengths to 1.3 μm. Nomarski optical microscopy and double crystal x-ray diffraction (XRD) measurements are used to investigate surface morphology, material quality and lattice-matched conditions. There is little or no 10K photoluminescence from the as-grown layers; alloy activation through rapid thermal annealing must be performed to obtain observable photoluminescence peaks. Annealing is also performed to reduce the resistivity of the as-grown layers. Once annealed, the undoped layers exhibited p-type carrier concentrations of 5.5×1017 cm−3 and mobilities of 50 cm2/Vs. The DC and frequency response performance characteristics of metal-semiconductor-metal (MSM) photodetectors fabricated on both as-grown and annealed InGaNAs layers are examined and compared to similar structures fabricated using GaAs and InGaAs/InP epitaxial materials.

Development of ZnSe-based white LEDs with Longer Lifetime over 10,000hrs

We have demonstrated ZnSe-based white LEDs with longer lifetime over 10,000hrs at 14.5A/cm2 by introducing an i-ZnMgBeSe/p-ZnMgSe double cladding structure, which combined a very thin i-ZnMgBeSe layer for suppressing electron overflow and p-ZnMgSSe for efficient p-type carrier concentration. By adopting the double cladding layer instead of the conventional p-ZnMgSSe cladding layer, rapid degradation is suppressed and the lifetime tendency is similar to the LEDs consisting of a III-V semiconductor system. The device simulation and the temperature dependence of optical power showed that the i-ZnMgBeSe layer played the main role in increasing electron confinement. Our experimental data and reliability test results indicate that the suppression of the electron overflow is essential to obtain long lifetime acceptable for truly practical use.

The role of surface adsorbates on electrical properties of MOVPE grown HgCdTe onto (0 0 1) GaAs substrates

Electrical properties of MOVPE grown HgCdTe layers on KOH pretreated GaAs substrates, were investigated. Rinsing the GaAs substrates with KOH, or NaOH in water solution before the growth have been used to reduce surface morphological defects (hillocks) density. It was found that the electrical properties depended on out diffusion of potassium during the growth. Ten micrometer thick annealed Hg 0.7Cd 0.3Te layers are measured to be p-type with p 77 ∼ mid 10 15 cm −3 and this is believed to be related to the average potassium concentration in the HgCdTe layer. SIMS analysis has shown that considerable amounts of potassium are incorporated at the interface of HgCdTe/CdTe and CdTe/GaAs. But a typical potassium concentration of as grown HgCdTe at surface is measured to be around low 10 14 cm −3. We could effectively reduce the residual potassium concentration and obtain HgCdTe with p-type carrier concentration of mid 10 14 cm −3 by inserting additional CdTe/HgCdTe layer before the growth of HgCdTe layer. This result significantly differed from the case of sodium pretreated sample, which shows the sodium concentration of mid 10 16 atoms cm −3 throughout full layer. Our result shows that MOVPE grown HgCdTe on KOH treated GaAs substrates could be used to fabricate large area forcal plane arrays which need hillock free surface as well as good electrical properties.

Novel Cladding Structure for ZnSe-based White Light Emitting Diodes with Longer Lifetimes of over 10,000 h

We have demonstrated ZnSe-based white light emitting diodes (LEDs) with longer lifetimes of over 10,000 h at 14.5 A/cm2 by introducing an i-ZnMgBeSe/p-ZnMgSe double cladding structure, which includes a very thin i-ZnMgBeSe layer for suppressing electron overflow and a p-ZnMgSSe layer for efficient p-type carrier concentration. By adopting the double cladding layer instead of only the conventional p-ZnMgSSe cladding layer, rapid degradation is suppressed and the lifetime tendency becomes similar to that of the LEDs consisting of a III–V semiconductor system. The device simulation and the temperature dependence of optical power showed that the i-ZnMgBeSe layer played the main role in increasing electron confinement. Our experimental data and reliability test results indicate that the suppression of the electron overflow is essential to achieve a long lifetime acceptable for practical use.

Room-temperature ferromagnetic semiconductor MnxGa1xSb

Ferromagnetic semiconductor MnxGa1-xSb single crystals were fabricated by Mn-ions implantation, deposition, and the post annealing. Magnetic hysteresis-loops in the MnxGa1-xSb single crystals were obtained at room temperature (300 K). The structure of the ferromagnetic semiconductor MnxGa1-xSb single crystal was analyzed by Xray diffraction. The distribution of carrier concentrations in MnxGa1-xSb was investigated by electrochemical capacitance- voltage profiler. The content of Mn in MnxGa1-xSb varied gradually from x = 0.09 near the surface to x = 0 in the wafer inner analyzed by X-ray diffraction. Electrochemical capacitance-voltage profiler reveals that the concentration of p-type carriers in MnxGa1-xSb is as high as 1 1021 cm-3, indicating that most of the Mn atoms in MnxGa1-xSb take the site of Ga, and play a role of acceptors.

Multiple-step annealing for 50% enhanced p-conductivity of GaN

In this article, multiple-step rapid thermal annealing (RTA) processes for the activation of Mg doped GaN are compared with conventional single-step RTA processes. The investigated multiple-step processes consist of a low temperature annealing step at temperatures between 350°C and 700°C with dwell times up to 5 min and a short time high temperature step. With optimized process parameters, and multiple-step processes, we achieved p-type free carrier concentrations up to 1–2×10 18 cm −3. The best achieved conductivity, so far, lies at 1.2 Ω −1 cm −1. This is a 50% improvement compared to conventional single-step process at 800°C, 10 min.

Comparison of carbon doping of InGaAs and GaAs by CBr 4 using hydrogen or nitrogen as carrier gas in LP-MOVPE

The p-type carrier concentration of MOVPE grown carbon doped InGaAs/InP and GaAs is investigated using H 2 and N 2 as carrier gas. Employing N 2 instead of H 2 halves the growth rate and diminishes the TMGa decomposition in the kinetically limited growth regime. The p-type carrier concentration of GaAs can be doubled by shifting to N 2. In N 2 ambient the maximal p-carrier concentration in InGaAs can be more than doubled compared to the maximal p-doping levels in H 2. Using N 2 as carrier gas it is possible to achieve p-type carrier concentrations in InGaAs/InP up to 1×10 19 cm −3 at temperatures as high as 550°C.

P- and N-type doping of GaN and AlGaN epitaxial layers grown by metalorganic chemical vapor deposition

Mg- and Si-doped GaN and AlGaN films were grown by metalorganic chemical vapor deposition and characterized by room-temperature photoluminescence and Hall-effect measurements. We show that the p-type carrier concentration resulting from Mg incorporation in GaN:Mg films exhibits a nonlinear dependence both on growth temperature and growth pressure. For GaN and AlGaN, n-type doping due to Si incorporation was found to be a linear function of the silane molar flow. Mg-doped GaN layers with 300K hole concentrations p ∼2×1018 cm−3 and Si-doped GaN films with electron concentrations n∼1×1019 cm−3 have been grown. N-type Al0.10Ga0.90N:Si films with resistivities as low as p ∼6.6×10−3 Ω-cm have been measured.

Achievement of low p-type carrier concentration for MOCVD growth HgCdTe without an annealing process

The electrical characteristics of as-grown epitaxial HgCdTe layers grown by metalorganic chemical vapor deposition were investigated. We propose a new cap layer in order to obtain as-grown HgCdTe layers with low p-type carrier concentration. The new cap layer called the “double-cap layer” consists of a graded Cd content Hg 1− x Cd x Te layer with x = 0.2–0.7 and a CdTe cap layer which was continuously grown at low temperature on the graded HgCdTe layer. The carrier concentration of HgCdTe layers with the new cap layer was about 3 × 10 16 cm −3. The p-type carrier concentration has been reduced further to 2 × 10 15 cm −3 (for x = 0.22) by lowering the growth temperature and increasing the partial pressure of Hg. This carrier concentration is lower than the estimated Hg vacancy concentration from considerations of the thermal equilibrium conditions.

Achievement of low p-type carrier concentration for MOCVD growth HgCdTe without an annealing process

Achievement of low p-type carrier concentration for MOCVD growth HgCdTe without an annealing process

Electrical fluctuations in HgCdTe introduced during quenching after annealing

HgCdTe epilayers used in infrared detectors have to be quenched after annealing in order to control the p-type carrier concentrations. It was found that μm-scale electrical fluctuations are introduced in the epilayer and around threading dislocation clusters during the quenching. Differential Hall measurements revealed an n-type region in the first 1 μm of the epilayer, followed by the p +-type (10 17 cm −3) region which gradually decreases with depth to 10 16 cm −3 in the next 5 μm. The fluctuating layer thickness decreased when the cooling rates increased. LBIC (laser-beam-induced current) images showed that p +-type electrical fluctuations and their dependence on the cooling rates are also observed around the threading dislocation clusters. The fluctuations are more than five times deeper than the former surface fluctuations. Simple estimations for the cooling process of the epilayers can qualitatively explain the experimental results.

Tertiarybutylarsine for Metalorganic Chemical Vapor Deposition Growth of High Purity, High Uniformity Films

We have performed an extensive study of GaAs, Al0.22Ga0.78As, and In0.16Ga0.84As grown using tertiarybutylarsine (TBA) in an ultra-high purity metalorganic chemical vapor deposition multi-wafer reactor. Key results include: high purity TBA AlGaAs layers with the lowest p-type carrier concentrations (4 × 1014 cm−3) reported to date; 4K photoluminescence bound exciton linewidths as narrow as 4.3 meV; C, O. Si, and S concentrations below the secondary ion mass spectrometry detection limit; and InGaAs/GaAs quantum wells with 20K PL linewidths as narrow as 3.5 meV. We also observe a strong dependence of growth rates and doping efficiency on group-V partial pressure, possibly due to a competition between excess group-V species and group-Ill or Si species for group-Ill surface sites. Finally, we demonstrate record uniformity using TBA with an AlGaAs thickness variation of only ±1.4% across a 4 inch wafer.

Growth and doping characteristics of ZnSeTe epilayers by MOCVD

Compositional control, band gap evaluation and acceptor doping characterization for ZnSeTe have been studied. Zinc selenotelluride layers were grown on GaAs (100) substrates by atmospheric metalorganic chemical vapor deposition. The composition of the ZnSexTe(1−x) solid is proportional to the gas phase composition when the VIII ratio is close to unity. Accurate band gap energy values for ZnSeTe epilayers were obtained at room temperature by photoreflectance spectroscopy. The bowing parameter is 1.647 eV. The p-type carrier concentration of ZnSeTe:As is drastically quenched with increasing Se incorporation. The quenching is possibly attributable to the lattice distortion.

Pulsed laser deposition of epitaxial AlN, GaN, and InN thin films on sapphire(0001)

Epitaxial aluminum nitride (AlN), gallium nitride (GaN), and indium nitride (InN) films were grown by pulsed laser deposition on sapphire(0001) substrates in high vacuum and in a nitrogen ambient of a few mTorr. The films were analyzed using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and room temperature van der Pauw-Hall measurements. The AlN films were single crystalline with AlN(0001)‖sapphire(0001) and AlN[11̄00]‖sapphire[112̄0]. The GaN films were also single crystalline with the same orientation as the AlN films. The InN films were found to have a preferred crystalline orientation with InN(0001)‖sapphire(0001) and InN[11̄00]‖sapphire[101̄0]. The AlN films were insulating. The GaN film grown in high vacuum had an n-type carrier concentration of 1 × 10 18 cm −3 and a mobility of 300 cm 2/V · s. The GaN film grown in 10 mTorr of N 2 had a p-type carrier concentration of 7.5 × 10 18 cm −3 and a mobility of 150 cm 2/V · s. The InN films grown in high vacuum and 5 mTorr of N 2 were both p-type with carrier concentrations of 6.5 × 10 20 and 4.7 × 10 19 cm −3, and mobilities of 30 and 240 cm 2/V · s, respectively.

Photon assisted growth of nitrogen-doped CdTe and the effects of hydrogen incorporation during growth

Nitrogen doping in CdTe epilayers grown by photo-assisted molecular beam epitaxy was demonstrated using an rf plasma source. The effect of the presence of atomic hydrogen during growth of undoped and nitrogen-doped CdTe was investigated. The layers were characterized using photoluminescence spectros-copy (PL), Hall effect, secondary ion mass spectroscopy (SIMS), Fourier transform infrared spectroscopy, and atomic force microscopy. PL confirmed the incorporation of nitrogen as acceptors. While p-type carrier concentrations greater than 1018 cm−3 were easily obtained, SIMS measurements indicated that nitrogen was concentrated near the undoped-doped and epilayer-substrate interfaces which complicates interpretation of activation efficiency. Hydrogen incorporation was found to be enhanced by the presence of nitrogen. Infrared absorption measurements strongly suggested the formation of N-H complexes. Hall measurements indicated that complexes are formed which are donor-like in nature. The presence of atomic hydrogen during growth radically changed the low temperature photoluminescence in both undoped and nitrogen-doped layers. Exciton-related luminescence was quenched at low temperature. Nitrogenrelated donor-acceptor pair luminescence was also absent from the N-doped hydrogenated layers, consistent with complex formation. Copper (a cation-site acceptor) donor-acceptor pair luminescence appeared to be enhanced by hydrogenation.

Growth and characterization of GaSb bulk crystals with low acceptor concentration

GaSb bulk single crystals with low acceptor concentration were grown from a bismuth solution by the traveling heater method. The result is isoelectronic doping by Bi which gives a variation of the opto-electronic properties as a function of grown length as well as a pronounced microscopic segregation. Photoluminescence spectra at 4K show a decrease of the natural acceptor during growth, which is confirmed by Hall measurements. The electrical properties of this isoelectronic doped GaSb are hole concentrations and mobilities of NA − ND = 1.7 × 1016 cm−3 and μ = 870 cm2Vs at room temperature and NA­ND = 1 × 1016 cm−3 and μ = 4900 cm2/Vs at 77K, respectively. The lowest p-type carrier concentration measured at 300K is NA − ND = 3.3 × 1015 cm−3