P. Kamyczek

A deep acceptor defect responsible for the yellow luminescence in GaN and AlGaN

In the present study, the electrical and optical properties of deep defects in p-i-n GaN junction and AlGaN/GaN heterojunction are investigated by means of the deep level transient spectroscopy (DLTS), Laplace DLTS, and electroluminescence (EL) techniques. We demonstrate that in both structures the yellow luminescence (YL) is a dominant band in the EL spectra recorded at room temperature. We correlate the YL band with the minority DLTS peaks observed at about 370 K. A gallium vacancy-related defect seems to be a probable candidate as to the origin of the defect. Another dominant majority peak observed in the DLTS studies was concluded to be linked with a donor-like defect in the upper half of the bandgap. The origin of the defect is discussed.

Deep traps in n-type GaN epilayers grown by plasma assisted molecular beam epitaxy

In this study, we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77 K–350 K. Undoped GaN layers were grown using the plasma-assisted molecular beam epitaxy technique on commercial GaN/sapphire templates. The quality of the epilayers was studied by micro-Raman spectroscopy (μ-RS) which proved the hexagonal phase and good crystallinity of GaN epilayers as well as a slight strain. The photoluminescence spectrum confirmed a high crystal quality by intense excitonic emission but it also exhibited a blue emission band of low intensity. DLTS signal spectra revealed the presence of four majority traps: two high-temperature and two low-temperature peaks. Using the Laplace DLTS method and Arrhenius plots, the apparent activation energy and capture cross sections were obtained. For two high-temperature majority traps, they were equal to E1 = 0.65 eV, σ1 = 8.2 × 10−16 cm2 and E2 = 0.58 eV, σ2 = 2.6 × 10−15 cm2 wher...

Influence of the AP MOVPE process parameters on properties of (In, Ga)(As, N)/ GaAs heterostructures for photovoltaic applications

GaAsN and InGaAsN semiconductor alloys with a small amount of nitrogen, so called dilute nitrides, are especially attractive for telecom lasers and very efficient multijunction solar cells applications. The epitaxial growth of these materials using MBE and MOVPE is a big challenge for technologists due to the large miscibility gap between GaAs and GaN. Additionally, elaboration of the growth process of quaternary alloys InGaAsN is more complicated than GaAsN epitaxy because a precise determination of their composition requires applying different examination methods and comparison of the obtained results. This work presents the influence of the growth parameters on the properties and alloy composition of the triple quantum wells 3×InGaAsN/GaAs grown by atmospheric pressure metal organic vapour phase epitaxy AP MOVPE. Dependence of the structural and optical parameters of the investigated heterostructures on the growth temperature and the nitrogen source concentration in the reactor atmosphere was analyzed. Material quality of the obtained InGaAsN quantum wells was studied using high resolution X-Ray diffraction HRXRD, contactless electro-reflectance spectroscopy CER, photoluminescence PL, secondary ion mass spectrometry SIMS, photocurrent PC and Raman RS spectroscopies, deep level transient spectroscopy DLTS and transmission electron microscopy TEM.

Laser irradiation effects on the CdTe/ZnTe quantum dot structure studied by Raman and AFM spectroscopy

Micro-Raman spectroscopy has been applied to investigate the impact of laser irradiation on semiconducting CdTe/ZnTe quantum dots (QDs) structures. A reference sample (without dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy technique on the p-type GaAs substrate. The Raman spectra have been recorded for different time of a laser exposure and for various laser powers. The spectra for both samples exhibit peak related to the localized longitudinal (LO) ZnTe phonon of a wavenumber equal to 210 cm−1. For the QD sample, a broad band corresponding to the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm−1. With increasing time of a laser beam exposure and laser power, the spectra get dominated by tellurium—related peaks appearing at wavenumbers around 120 cm−1 and 140 cm−1. Simultaneously, the ZnTe surface undergoes rising damage, with the formation of Te aggregates at the pinhole edge as reveal atomic force microscopy observations. Local temperatu...

Structural and optical characterization of GaN nanowires

Optical properties of GaN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy on Si(111) substrates were studied with the use of micro-Raman spectroscopy and photoluminescence. Two types of NWs, hereafter labeled as A and B, grown with different values of Ga flux were studied. Morphology of the samples was probed by high resolution scanning electron microscopy. It was found that large Ga flux has led to a partial coalescence of nanowires in sample A. Reduction of Ga flux during growth of sample B resulted in an ensemble of separated nanowires. Micro-Raman and photoluminescence spectra were taken under illumination of 325 nm He-Cd laser line. Micro-Raman data reveal hexagonal phase of GaN NWs as well as a slight strain of Si substrate. Photoluminescence data yield that ensembles of separated NWs in sample B are defect free, whereas the spectra for coalesced wires in sample A exhibit both broad yellow luminescence band and defect-related band centered around 3.36 eV. Moreover, it was found that ...

Deep levels in GaN studied by deep level transient spectroscopy and Laplace transform deep-level spectroscopy

In this study we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77–350 K. Si-doped GaN layers were grown by Molecular Beam Epitaxy technique (MBE) on sapphire substrates. DLTS signal spectra revealed the presence of four majority traps: two hightemperature and two low-temperature peaks. Using LDLTS method and Arrhenius plots the activation energy and capture cross sections were obtained. For two high-temperature majority traps they are equal to E1 = 0.65 eV, σ1 = 8.2 × 10−16cm2 and E2 = 0.58 eV, σ2 = 2.6 × 10−15 cm2 whereas for the two low-temperature majority traps E3 = 0.18 eV, σ3 = 9.72 × 10−18 cm2 and E4 = 0.13 eV, σ4 = 9.17 × 10−18 cm2. It was also found that the traps are related to point defects. Possible origin of the traps was discussed and the results were compared with the data found elsewhere [1–5].

Electro-optical properties of diluted GaAsN on GaAs grown by APMOVPE

In this paper we report on the optical and electrical studies of single GaAs1−xNx epitaxial layers grown on GaAs substrates by means of atmospheric pressure metal organic vapour phase epitaxy (APMOVPE). Three kinds of samples with 1.2 %, 1.6 % and 2.7 % nitrogen content were studied. Optical properties of the layers were investigated with the use of room temperature transmittance and reflectance measurements. Subsequently Schottky Au-GaAs1−xNx contacts were processed and characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements within 80–480 K temperature range. From the I-V and C-V characteristics the ideality factor, series resistance and built-in potential were determined. Obtained diodes can be used for further studies on defects with the use of DLTS method.

Investigation of deep-level defects in InGaAsN/GaAs 3xQWs structures grown by AP-MOVPE

We have investigated deep-level defects in InGaAsN/GaAs 3xQW structures by means of conventional as well as high-resolution deep level transient spectroscopy (DLTS). The three samples were grown by atmospheric pressure metalorganic vapour phase epitaxy (AP-MOVPE) in different growth temperatures (566°C, 575°C and 585°C). The DLTS measurements revealed four electron traps E1 (0.17-0.24 eV), E2 (0.36-0.38 eV), E3 (0.46-0.49 eV) and E4 (0.81-0.84 eV) and one hole trap H1(0.8 eV) in our structures. The electron trap E1 was associated with N-related complexes while the other electron traps with native defects, usually observed in GaAs-based structures EL6, EL3 and EL2, respectively. Finally, the trap E2 and H1, observed in the structure grown at lowest temperature, were associated with the same trap, which can act as both an electron and hole trap. It was thus concluded that E2/H1 may be a generation-recombination center.

Characterization of Diamond-like Carbon (DLC) films deposited by RF ICP PECVD method

The work presents the results of a research carried out with Plasmalab Plus 100 system, manufactured by Oxford Instruments Company. The system was configured for deposition of diamond-like carbon films by ICP PECVD method. The deposition processes were carried out in CH4 or CH4/H2 atmosphere and the state of the plasma was investigated by the OES method. The RF plasma was capacitively coupled by 13.56 MHz generator with supporting ICP generator (13.56 Mhz). The deposition processes were conducted in constant value of RF generator’s power and resultant value of the DC Bias. The power values of RF generator was set at 70 W and the power values of ICP generator was set at 300 W. In this work we focus on the influence of DLC film’s thickness on optical, electrical and structural properties of the deposited DLC films. The quality of deposited DLC layers was examined by the Raman spectroscopy, AFM microscopy and spectroscopic ellipsometry. In the investigated DLC films the calculated sp3 content was ranging from 60 % to 70 %. The films were characterized by the refractive index ranging from 2.03 to 2.1 and extinction coefficient ranging from 0.09 to 0.12.

Characterisation of AP-MOVPE grown (Ga, In)(N, As) structures by Raman spectroscopy

Over the last few years, ternary and quaternary semiconductor compounds containing (Ga, In) and (N, As) elements become subject of many studies. Both, indium and nitrogen, lowers the band gap of gallium arsenide, but their influence on lattice parameter is compensated. As a result it is possible to deposit epitaxial layers of 1 eV , or less, material which is matched to GaAs substrate. GaAs technology is well known and much cheaper than more sophisticated phosphorus alloys. Optoelectronic devices composed of dilute nitrides materials can be widely used as a telecommunication lasers, photodetectors or even photovoltaic cells. Investigated samples were performed using atmospheric-pressure MOVPE system with AIXTRON AIX200 R-and-D reactor. GaNAs layers were deposited as bulk layers, while GaInNAs material grown as bulk and additionally as quantum wells with GaAs barriers. Gallium arsenide substrates were utilized. Studies were performed utilizing Raman spectroscopy at room temperature. Phonons were excited using 514 nm Ar+ laser. Characteristic for such structures GaN-like local vibrational mode was observed to change its position with changing nitrogen concentration. GaAs-like longitudinal optic phonon also was investigated. As a result an attempt to measure nitrogen concentration in mentioned materials using Raman spectroscopy was performed.