M. Kučera

Formation of interfaces in InGaP/GaAs/InGaP quantum wells

Abstract Interfaces (IFs) of In 0.485 Ga 0.515 P/GaAs/In 0.485 Ga 0.515 P quantum wells (QWs) grown by LP-MOVPE technology were studied, and a significant influence of growth conditions on properties of the QWs was observed and theoretically analysed. The paper shows that a low-band-gap ternary or quaternary interlayer (IL) between the bottom InGaP barrier and the GaAs well layer is the general reason for the deterioration of the IF quality. Such an IL forms spontaneously during the growth. Its formation can be enhanced using an inappropriate growth switching sequence and temperature. An As-to-P exchange process was found to be the dominant mechanism of the formation of the IL at a growth temperature of 560°C. An In 0.485 Ga 0.515 As monolayer (ML), created by the P-to-As exchange mechanism, is always present at the InGaP/GaAs IF. Even such an ML can considerably deteriorate properties of the QW. A proper switching sequence with thin GaP ILs grown at the IFs can eliminate the influence of spontaneous intermixing processes. We have calculated the quantized energy levels of QWs, which contained IL of various compositions and thicknesses. The results of calculation were compared with experimentally determined energies obtained from photoluminescence (PL) measurements. Based on this comparison, thicknesses of the ILs were estimated. Only small influence of As interdiffusion into the barriers and a negligible influence of indium carry-over into the GaAs well material were observed. From an analysis of the results it follows that about 1xa0ML thick ILs are spontaneously formed at the growth conditions used.

HYDROGENATED AMORPHOUS SILICON CARBON NITRIDE FILMS PREPARED BY PECVD TECHNOLOGY: PROPERTIES

Hydrogenated amorphous silicon carbon nitride films were grown by plasma enhanced chemical vapor deposition (PECVD) technique. The flow rates of SiH4 , CH4 and NH3 gases were 6 sccm, 30 sccm and 8 sccm, respectively. The deposition temperatures were 350, 400 and 450 ◦C. The RBS and ERD results showed that the concentrations of Si, C, N and H are practically the same in the films deposited at substrate temperatures in the range 350-450 ◦C. In photoluminescence spectra we identified two peaks and assigned them to radiative transitions typical for amorphous materials, ie band to band and defect-related ones. The electrical characterization consists of I(V ) measurement in sandwich configuration for voltages up to 100 V. From electrical characterization, it was found that with increased deposition temperature the resistivity of the amorphous SiCN film was reduced.

Study of narrow InGaP/(In)GaAs quantum wells

Narrow InGaP/GaAs/InGaP and InGaP/InGaAs/InGaP quantum wells (QWs) prepared by MOVPE were studied by photoluminescence and HRXRD in this work. A detailed analysis of the results has shown the presence of band gap fluctuations at the interfaces in the InGaP/(In)GaAs/InGaP system. A series of experiments with various thickness of QWs from 1 to about 19 monolayers allowed us to distinguish various influences on the interface quality. It is shown that diffusion plays only a negligible role at our growth temperature of 560°C. Immiscibility in a thin In1−xGaxAs1−yPy interlayer that forms at the interface along with surface kinetic processes are suggested to be the driving force for composition variations at the interfaces. The impact of MOVPE growth techniques minimising the inhomogeneities at the interface is discussed.

InGaP/GaAs/InGaP quantum wires grown on pre-patterned substrates by MOVPE

Abstract We prepared InGaP/GaAs/InGaP V-groove heterostructures incorporating quantum wires using metalorganic chemical vapour deposition technique. Influence of the growth temperature on the facetting and growth rate according to the crystallographic orientation was studied. Low temperature photoluminescence was used for characterisation of quantum structures prepared. To enhance a photoluminescence signal from quantum wire, the two step Au evaporation was used with the aim to suppress PL signals from the sidewalls.

Sulphur doping of GaSb grown by atmospheric pressure MOVPE

Abstract Sulphur-doped GaSb epitaxial layers are grown on GaSb and GaAs substrates by atmospheric pressure MOVPE. Trimethylgallium and trimethylantimony are used as the Ga and Sb sources, respectively. Hydrogen sulphide (1% H2S diluted in hydrogen) is employed as the sulphur source. The mole fraction of H 2 S in the reactor ranging from 6.1 × 10 −6 to 1.2×10 −4 results in the hole concentrations from 2.8×10 17 to 2.5×10 18 cm −3 , respectively. Low temperature ( T = 5 K) photoluminescence measurements show a sulphur-related transition S 1 near 732 meV indicating that sulphur is successfully incorporated into GaSb. The PL spectra of the samples grown with a H 2 S mole fraction larger than 6.2 × 10 −5 consist only of a native acceptor transition A and a sulphur-related transition S 1 The position of S 1 transition is independent of the H 2 S mole fraction. The ratio of the intensity of the sulphur-related transition S 1 to the that of the transition A increases from 0 up to 1.5 with increasing H 2 S mole fraction.

Photoluminescence characterization of InGaP/GaAs/InGaP quantum wires

We investigated the photoluminescence of InGaP/GaAs/InGaP heterostructures with the aim to prepare quantum wires by the epitaxial overgrowth of V-groove patterned substrates. Planar and V-groove patterned GaAs semiinsulating substrates were used for epitaxial growth in a low-pressure MOVPE equipment with a horizontal reactor. Low temperature photoluminescence measurements show that the composition of the InGaP ternary compound prepared on the patterned substrates is shifted to a higher InP mole fraction compared with the planar ones. On the other hand, the measurement on the V-grooved samples showed that the PL peak is shifted to higher energies (i.e. to the higher amount of Ga), which indicates a change in the ternary composition of about 5%. Crystalline quality of the overgrown structures was studied by transmission electron microscopy. Both, photoluminescence and photoluminescence polarization measurement show that quantum wires can be successfully prepared in the InGaP/GaAs/InGaP system.

Preparation of stair-step grooves by wet etching of AlAs/GaAs heterostructures and MOCVD growth of QWR

The possibility of preparing stair-step V- or U-grooves into a GaAs/AlAs heterostructure by isotropic and anisotropic wet chemical etching was studied. Several patterned structures with well-defined (100) planes of stairs were overgrown by MOCVD with the aim to realize quantum wires (QWRs) due to the selectivity of growth on these planes. This approach should allow for adjusting lateral and vertical dimensions independently as well as for a simple regulation of the density of QWRs. Samples were subsequently characterized by photoluminescence (PL), and it was supposed that the observed red shift could result from the presence of the QWRs.

Photoreflectance study of the role of a thin AlO x layer in a GaAs surface passivation and the Schottky barrier forming

We studied UN+-type GaAs(100) samples covered with a thin AlOx passivation layer and with Ni metallization of variable thicknesses. Photoreflectance spectroscopy was used to measure the electric field in the undoped part of the samples. The position of the surface Fermi level, the amount of the electric charge trapped at the surface, and the effect of the pinning were investigated. The AlOx layer did not change the pinning compared to the UN+ sample without AlOx. After metallisation, the barrier height was markedly higher in the MIS structures with AlOx, indicating a much weaker pinning than in the structures with native oxides. Several samples covered with metallisation layers of different thickness were prepared. The highest barrier was reached for the 3 nm Ni / 3 nm Au stack.

Electron cyclotron resonance plasma technology of silicon carbon nitride thin films

Silicon carbon nitride films were grown at various deposition temperature from 350 to 550°C by means of electron cyclotron resonance (ECR) plasma deposition with gas mixture: 5% SiH4 in N2(20 sccm), CH4(10 sccm). A p-type silicon wafer with resistivity 2-7 Ωcm and (100) orientation was used as the substrate for the SiCN films. The concentration of elements in the SiCN films was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical method simultaneously. Chemical compositions were analysed by infrared (IR) spectroscopy. Photoluminescence (PL) spectra were measured at 293 K. The concentration of hydrogen was decreased with increasing deposition temperature. The IR results showed the presence of Si-C, Si-N, Si-H, C-H, C-N, N-H and Si-O bonds. The PL results showed increassing PL intensity with increasing a sample deposition temperature from 350 to 450°C and decreasing PL intensity with increasing a sample deposition temperature from 450 to 550°C.

Epitaxial Growth of GaP/InxGa1-xP (xIn ≥ 0.27) Virtual Substrate for Optoelectronic Applications

Epitaxial Growth of GaP/InxGa1-xP (xIn ≥ 0.27) Virtual Substrate for Optoelectronic Applications Compositionally graded epitaxial semiconductor buffer layers are prepared with the aim of using them as a virtual substrate for following growth of heterostructures with the lattice parameter different from that of the substrates available on market (GaAs, GaP, InP or InAs). In this paper we report on the preparation of the step graded InxGa1-xP buffer layers on the GaP substrate. The final InxGa1-xP composition xIn was chosen to be at least 0.27. At this composition the InxGa1-xP band-gap structure converts from the indirect to the direct one and the material of such composition is suitable for application in light emitting diode structures. Our task was to design a set of layers with graded composition (graded buffer layer) and to optimize growth parameters with the aim to prepare strain relaxed template of quality suitable for the subsequent epitaxial growth.