In0.145Ga0.855AsySb1−y semiconductor alloys were grown on GaSb(100) substrates by varying the As content by liquid phase epitaxy (LPE). We demonstrated that the growth mechanism of these quaternary ...alloys is mainly constituted by two stable bonding configurations, Ga−Sb and In−As. These quaternary alloys showed a high crystalline quality due to the nearly lattice-matched epitaxial growth to the GaSb substrate. We identified a tensile strain of the In0.145Ga0.855AsySb1−y alloys on the GaSb substrate, strain that increases with the As content. In the bulk region of these crystalline alloys it was noticed a greater fonon-plasmon coupling than in the surface space-charge region. In addition, we found that the band gap energy of the In0.145Ga0.855AsySb1−y alloys can be easily engineered in the near infrared by varying the As content. Excitonic transitions were observed in these quaternary alloys, whose energy decreases with the As content. We employed a theoretical method that considers spin-orbit coupling for the determination of the band gap energy, which is in agreement with experimental results. These findings provide an important understanding of the growth dynamics, and of the optical and structural properties of the In0.145Ga0.855AsySb1−y crystalline alloys by varying the As content for near infrared applications using the band gap engineering.
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•In0.145Ga0.855AsySb1−y alloys were grown on GaSb substrate by varying the As content.•The quaternary alloys were grown by Liquid Phase Epitaxy (LPE).•The growth mechanism of these alloys is mainly constituted by Ga−Sb and In−As.•The excitonic transition energies of the alloys decrease with the As content.
In this work, ZnO nanorods were grown by chemical bath deposition technique on substrates which were previously deposited with ZnO seed layers (SL’s). The seed layercs were deposited by ultrasonic ...spray pyrolysis at different deposition temperatures. The average grain size of seed layers was 129, 140 and 48.4 nm for seed layers deposited at 250, 350 and 450 °C, respectively. Nanorods grown on SL´s deposited at 250 and 350 °C have parallel orientation as well as perpendicular orientation to the substrate. On the other hand, nanorods grown on seed layer deposited at 450°C have perpendicular orientation and have a uniform size and shape. The average rod diameters decreased as the deposition temperature of seed layer increased, from 308 to 78 nm. Nanorods exhibit good crystalline quality and preferential orientation in the (002) plane, as well as green photoluminescence at room temperature for UV excitation wavelength. CO
2
gas sensing properties of both as deposited seed layers and nanorods were obtained and reported in this work. Increment in deposition temperature showed a substantial increase in CO
2
sensing response for both SL’s and nanorods. Also, ZnO nanorods sensing response showed different advantages in comparison with ZnO seed layers such as higher sensing response, 9 times faster response and recovery times and a complete resistance recovery which makes its utilizable in practical monitoring devices.
The structural and electrical properties of Mg-doped cubic GaN epi-layers grown by plasma-assisted molecular beam epitaxy (PAMBE) near Ga rich conditions are investigated. The diffraction of ...high-energy reflected electrons (RHEED) in situ, in addition to structural studies of X-ray diffraction, show that the fraction of hexagonal and crystal twinning inclusions decreases when the Mg flux increases. The condition for the higher incorporation of Mg where the electrical properties are optimized is highly sensitive to the flow ratio Mg/Ga. The p-doping level steadily increases with increasing Mg flux. The Mg concentration obtained by secondary ion mass spectroscopy (SIMS) from samples grown at Mg temperatures from 200 °C to 700 °C are in a range between 2 × 1019 to 2 × 1020 atoms/cm3. The highest mobility and p-type doping level achieved, determined from Hall measurements, were 28.2 cm2/V-s and 2 × 1019 cm−3, respectively. We corroborate that the Mg doped c-GaN films are suitable for the construction of optoelectronic devices based on cubic III-Nitrides.
The impact of annealing on the emission of InAs quantum dots (QDs) has been investigated in the GaAs/Al
0.30
Ga
0.70
As structures with different compositions of the quantum well (QW) layers covered ...of QDs: GaAs or Al
0.10
Ga
0.75
In
0.15
As. The heat treatments of the QD structures were carried out at 640°C or 710°C for 2 h in an argon atmosphere. To estimate the compositions of QDs and capping QWs, photoluminescence (PL) and high-resolution X-ray diffraction have been applied. The QD structure with the Al
0.1
Ga
0.75
In
0.15
As capping QWs has been characterized by a lower energy of the ground state emission (≈ 1.30 µm, 300°K), its highest intensity and the smaller full width at half maximum, compared to the QD structure with GaAs capping QWs. The extinction of the integrated PL intensity about 80 times was detected in the range 10–400 K for the QD structure with Al
0.10
Ga
0.75
In
0.15
As capping compared to this extinction more than 1000 times detected in the QD structure with GaAs capping. The advantages obtained in the QD structure with Al
0.1
Ga
0.75
In
0.15
As capping are attributed to the lower mismatch and stresses at the capping QW/InAs QD interfaces, as well as the higher chemical binding energy of the Al-As bonds, compared to their value for Ga-As, which decreases the interdiffusion efficiency of the Ga/In atoms.
A new method of making ohmic contacts to p-GaN Hernández-Gutierrez, C.A.; Kudriavtsev, Yu; Mota, Esteban ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2016, Letnik:
388
Journal Article
Recenzirano
•Low resistance Ohmic contacts preparation is based on low energy high dose In+ ion implantation into Metal/p-GaN to achieve a thin layer of InxGa1-xN just at the interface.•The specific ohmic ...contact was reduced from 10−2Ωcm2 to 2.5×10−4Ωcm2.
The structural, chemical, and electrical characteristics of In+ ion-implanted Au/Ni, Au/Nb and Au/W ohmic contacts to p-GaN were investigated. After the preparation of Ni, Nb and W electrode on the surface of p-GaN, the metal/p-GaN contact interface was implanted by 30keV In+ ions with an implantation dose of 5×1015ions/cm2 at room temperature to form a thin layer of InxGa1-xN located at the metal-semiconductor interface, achieved to reduce the specific contact resistance due to the improving quantum tunneling transport trough to the structure. The characterization was carried out by high-resolution X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and secondary ion mass spectrometry to investigate the formation of ternary alloy, re-crystallization by rapid thermal annealing process after In+ implantation, and the redistribution of elements. The specific contact resistance was extracted by current-voltage (I-V) curves using transmission line method; the lowest specific contact resistance of 2.5×10−4Ωcm2 was achieved for Au/Ni/p-InxGa1-xN/p-GaN ohmic contacts.
•Cubic GaN samples were grown on GaAs(001) substrates by using an As4 overpressure during the nucleation layer.•The relaxation process of c-GaN affects the purity of cubic phase.•Higher purity of ...c-GaN was obtained on (11¯1)N and (1¯11)N planes.•PL measurements showed transitions corresponding to c-GaN.
Cubic GaN samples on GaAs(001) substrates were grown by RF-plasma-assisted molecular beam epitaxy (RF-MBE), an As4 overpressure was employed during the nucleating layer. We found that the relaxation process of c-GaN during the nucleating layer, affects the purity of cubic phase. Higher cubic phase of GaN was obtained for samples that initiated the relaxation process after some monolayers (8ML) of growth, as a result of better stabilization of the cubic layer. The relaxation process depends on the As4 overpressure over the growth surface and on the growth temperature. The structural properties of c-GaN characterized by transmission electron microscopy (TEM) and high resolution X-ray diffraction (HR-XRD) have evidenced the purity of cubic phase in the first nanometer of growth, and also the formation of the hexagonal inclusions after several nanometers of growth from the stacking faults on the {111} planes. From an estimation of the hexagonal content by X-ray reciprocal space mapping (RSM), we found a lower hexagonal component on the (11¯1)N and (1¯11)N planes. The highest purity of cubic GaN was 98.7% along the {111}N planes for sample grown at 720°C. Photoluminescence measurements also demonstrated the high purity of the cubic phase of this sample, no emission of hexagonal inclusion was detected.
InxGa1−xN (001) ternary alloys were grown on GaN/MgO (100) substrates in a plasma assisted molecular beam epitaxy system. We determined the in-plane 001 and in-growth 110 lattice parameters, as well ...as the bulk lattice parameter of the alloys for different In concentrations by high resolution X-ray diffraction. The In concentration was determined assuming Vegard׳s law for the alloy lattice parameter. The optical energy gap of InxGa1−xN has been determined by transmittance measurements from absorption edges for several In concentrations. Our results show that the alloys have a direct band gap for all In concentrations and a bowing parameter b=1.84.
•Cubic InxGa1−xN.•Bulk lattice parameter.•Optical band gap.•Molecular beam epitaxy.
Heterostructures, which incorporate GaAs/InGaAs/GaAs quantum wells and are doped with spatially remote monatomic Mn layers, are formed on GaAs(001) substrate under conditions of multilayer buildup by ...the method of molecular-beam epitaxy. Combined studies of the obtained samples were performed by the method of secondary-ion mass spectrometry, by measurements of X-ray diffraction, and using a transmission electron microscope. The heterostructures under study with a doping impurity concentration amounting to 0.5 single layers are elastically stressed and demonstrate planar clearly defined interfaces without visible extended or point defects. A method for visualization of the distribution of the manganese concentration in the three-dimensional GaAs matrix in the vicinity of a quantum well is suggested. According to experimental results, there is a probability for manganese diffusion into the GaAs/InGaAs/GaAs quantum well when the critical thickness of the GaAs buffer layer is decreased to a value smaller than 3 nm.
In this report, the performance of a particular pixel's architecture is evaluated. It consists mainly of an optical sensor coupled to an amplifier. The circuit contains photoreceptors such as ...phototransistors and photodiodes. The circuit integrates two main blocks: (a) the pixel architecture, containing four p-channel transistors and a photoreceptor, and (b) a current source for biasing the signal conditioning amplifier. The generated photocurrent is integrated through the gate capacitance of the input p-channel MOS transistor, then converted to voltage and amplified. Both input transistor and current source are implemented as a voltage amplifier having variable gain (between 10dB and 32dB). Considering characterisation purposes, this last fact is relevant since it gives a degree of freedom to the measurement of different kinds of photo-devices and is not limited to either a single operating point of the circuit or one kind and size of photo-sensor. The gain of the amplifier can be adjusted with an external DC power supply that also sets the DC quiescent point of the circuit. Design of the row-select transistor's aspect ratio used in the matrix array is critical for the pixel's amplifier performance. Based on circuit design data such as capacitance magnitude, time and voltage integration, and amplifier gain, characterisation of all the architecture can be readily carried out and evaluated. For the specific technology used in this work, the spectral response of photo-sensors reveals performance differences between phototransistors and photodiodes. Good approximation between simulation and measurement was obtained.
