Wojciech Dawidowski

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.

Influence of rapid thermal annealing on optical properties of (In, Ga)(As, N)/GaAs quantum wells

Dilute nitride (In, Ga)(As, N) alloys grown on GaAs substrate are a very attractive materials for optoelectronics. In this work we compare the optical properties of (In, Ga)(As, N)/GaAs triple quantum well grown by atmospheric pressure metal organic vapour phase epitaxy. As grown and annealed structures were investigated by means of photoluminescence and contactless electroreflectance spectroscopies. Energies of fundamental transition from each measurement were determined and compared, moreover the value of Stokes shift was assigned and discussed.

Structural Characterization of Doped Thick Gainnas Layers - Ambiguities and Challenges

Abstract GaInNAs alloys are mostly used as an active part of light sources for long wavelength telecom applications. Beside this, these materials are used as thin quantum wells (QWs), and a need is to grow thick layers of such semiconductor alloys for photodetectors and photovoltaic cells applications. However, structural characterization of the GaInNAs layers is hindered by non-homogeneity of the In and N distributions along the layer. In this work the challenges of the structural characterization of doped thick GaInNAs layers grown by atmospheric pressure metalorganic vapour phase epitaxy (APMOVPE) will be presented

LP-MOVPE growth and properties of high Si-doped InGaAs contact layer for quantum cascade laser applications

Abstract The work presents doping characteristics and properties of high Si−doped InGaAs epilayers lattice−matched to InP grown by low pressure metal−organic vapour phase epitaxy. Silane and disilane were used as dopant sources. The main task of investigations was to obtain heavily doped InGaAs epilayers suitable for usage as plasmon−confinement layers in the construction of mid−infrared InAlAs/InGaAs/InP quantum−cascade lasers (QCLs). It requires the doping concentration of 1×1019 cm–3 and 1×1020 cm–3 for lasers working at 9 μm and 5 μm, respectively. The electron concentration increases linearly with the ratio of gas−phase molar fraction of the dopant to III group sources (IV/III). The highest electron concentrations suitable for InGaAs plasmon−contact layers of QCL was achieved only for disilane. We also observed a slight influence of the ratio of gas−phase molar fraction of V to III group sources (V/III) on the doping efficiency. Structural measurements using high−resolution X−ray diffraction revealed a distinct influence of the doping concentration on InGaAs composition what caused a lattice mismatch in the range of –240 ÷ –780 ppm for the samples doped by silane and disilane. It has to be taken into account during the growth of InGaAs contact layers to avoid internal stresses in QCL epitaxial structures.

Scanning capacitance microscopy characterization of AIIIBV epitaxial layers

Abstract The applicability of scanning capacitance microscopy (SCM) technique for chosen electrical properties characterization of AIIIBV structures fabricated by Metalorganic Vapor Phase Epitaxy (MOVPE) was examined. The calibration curves for quantitative characterization of doping levels in GaAs layers were created. The AlGaN/GaN/Si heterostructures for high electron mobility transistor fabrication and InGaAs tunnel junction for tandem solar cell characterization were presented. The crucial factors of measurement conditions which could influence the obtained results were also discussed.

Electrophysical Properties of GaAs P–I–N Structures for Concentrator Solar Cell Applications

Abstract This paper is dedicated to electro-physical characterisation of a GaAs p-i-n structure grown for solar cell applications, which was carried out by light and dark current-voltage (I–V) and Deep Level Transient Fourier Spectroscopy (DLTFS) methods. The conversion efficiency and open-circuit voltage were determined from I–V measurement at 1 and 20× sun light concentrations. Three electron like defects TAn1, TAn2, TDn and one hole like defect TBp obtained by DLTFS measurements were confirmed. The origin of these defect states was stated as native GaAs impurities.

DLTFS INVESTIGATION OF InGaAsN/GaAs TANDEM SOLAR CELL

Abstract In this paper authors present the results of identification of emission and capture processes in tandem solar cell structures based on quaternary InGaAsN semiconductor alloys by DLTFS (Deep Level Transient Fourier Spectroscopy) and by ana- lytical evaluation processes. The energies of five trap levels ET1=0.77 eV, ET2=0.47 eV, ET3=0.64 eV, HT1=0.62 eV and HT2=0.53 eV were identified with reliable accuracy. These values were obtained by available analytical procedures, verified by simulations and confirmed by reference structures with basic layer types and compared with possible reference trap data. Native structural defects in GaAs were stated as the origin of these deep energy levels

GaInNas/GaAs QW Based Structures to Compensate Parasitic Effect of Quantum-Confined Stark Effect in Photodetector Applications

The inhomogeneities of multicomponent semiconductor alloys, as well as phase segregation, can be utilized for enhancement of photodetector absorption properties and thus its efficiency. In this paper, the influence of external electric field on the probability of light absorption in the GaInNAs quantum well is discussed. Both phenomenon: indium and nitrogen composition gradient as well as step-like quantum well are applied to design the QW with compensation of the Quantum-Confined Stark Effect (QCSE) Parasitic effect of QCSE results from decrease of the wave functions overlapping in the QWs placed in reverse biased junction, which finally decrease the efficiency of the photodetector.

DLTS study of electrically active defects in triple quantum well InGaAsN/GaAs heterostructures

Deep Level Transient Fourier Spectroscopy study of charge carrier emission from quantum wells and electrically active defects in triple quantum well InGaAsN/GaAs heterostructures is discussed. Main attention is focused on the comparison and evaluation of measured spectra and to state the conditions of quantum well charge carrier emission identification. The presence of several deep energy levels and their parameters typical for GaAs are reported.

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.