Beata Sciana

Epitaxial Growth and Characterisation of Silicon Delta-Doped GaAs, AlAs and Alx Ga1-xAs

Investigation of MOVPE growth of silicon δ-doped GaAs, AlAs and Al x Ga 1-x As epilayers and different methods used for their characterisation are presented. The epitaxial structures were grown in an atmospheric pressure horizontal AIX 200 Aixtron reactor. Delta doping was formed by SiH 4 introduction during the growth interruption. The influence of the growth temperature and Al x Ga 1-x As composition on delta-doping characteristics, carrier concentration and mobility is discussed. Properties of the investigated Si δ-doped structures were examined using capacitance-voltage measurements, Van der Pauw-Hall measurements (300K, 77K), photocurrent measurements, photoreflectance spectroscopy and X-ray measurements.

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.

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

Influence of the MOVPE growth parameters on the properties of InGaAsN/GaAs MQW structures for solar cells application

This work presents the epitaxial growth of undoped multiple quantum well (MQW) - 3 × In_yGa_1-yAs_1-xN_x/GaAs - structures obtained by atmospheric pressure metalorganic vapour phase epitaxy (APMOVPE). The relations between the hydrogen flow rate through the bubblers with TBHy, TMGa, TMIn and the composition of the resulting In_yGa_1-yAs_1-xN_x films were investigated. The influence of the growth temperature on the quantum well In_yGa_1-yAs_1-xN_x parameters were observed. Based upon this experiment, the technology parameters were estimated. These results were applied to the optimization of the hydrogen flow rate through the bubblers with TBHy, TMGa, TMIn and temperature for the growth of quantum well of In_yGa_1-yAs_1-xN_x.

The influence of the electrolyte-semiconductor interface on the doping profile measurement of a GaAs structure

The electrical behavior of the 0.1 M Tiron electrolyte-GaAs interface has been investigated. Attention is centred upon the properties of the electrolyte-GaAs interface and its influence on the capacitance-voltage measurements. Electrical properties of the interface were measured by electrochemical C-V techniques and impedance spectroscopy.

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.

Low temperature investigation of electrical and optical properties of InGaAsN/Gas QW Schottky barrier photodetectors

This work presents electrical and optical properties of Schottky barrier photodetectors containing the triple quantum well (MQW) InGaAsN/GaAs structures grown by atmospheric pressure metal organic vapour phase epitaxy. The peaks corresponding to optical transitions in MQW were identified by photocurrent spectroscopy and compared with simulations. The measurements revealed that there are two embedded and overlapped QW which can be simulated as InxGa1-xAs1-yNy/GaAs QW and InxGa1-xAs/GaAs QW with appropriate width and composition. This effect can be assigned to the interdiffusion between QW and GaAs during the structure growth. The low temperature spectral measurements revealed the shift and intensity of optical transitions in particular QWs.

Deep levels in InGaAsN/GaAs and InGaAs/GaAs heterojunctions

This paper highlights the deep level transient spectroscopy investigation of the triple quantum well InGaAsN/GaAs and InGaAs/GaAs heterostructures grown by atmospheric pressure metal organic vapour phase epitaxy (APMOVPE). The main differences of these typical triple quantum well structures are: nitrogen concentration in InyGa1-yAs/GaAs heterostructures, thickness of UD InyGa1-yAs1-xNx quantum wells, indium concentration and thickness of UD GaAs barrier. The three electron deep levels ET1 (0.472 eV), ET2 (0.974 eV) and ET3 (0.572 eV) were identified. The 0.36 % presence of nitrogen in structure NI51n inhibits defect ET1 and creates the trap ET2 with very high trap concentration.

Tunnel junction technology for multijunction solar cell applications

Solar cells are very promising renewable resource. High efficiency of AIIIBV based solar cells are achieved in multijunction constructions. The technology of these devices is very difficult due to the complex electrical and optical interactions between the different semiconductor layers. Usually, the individual subcells are interconnected via Esaki tunnel diodes. This work presents the technology and computer modelling of GaAs based tunnel diodes which will be applied in tandem GaAs/InGaAs solar cells. Designed structures were grown by atmospheric pressure metal organic vapour phase epitaxy. Simulation results as well as dopant profiles and measured DC I-U characteristics of the obtained tunnel diodes are presented and discussed.

AP-MOVPE growth and characterization of GaAs1-xNx epilayers

Nitrogen incorporation into GaAs epilayers has received interest especially due to band gap decreasing of resultant material. Small fraction of nitrogen makes GaAs1-xNx useful material for optoelectronic devices grown on GaAs substrates. However, achieving high quality of GaAs1-xNx/GaAs heterostructures requires MBE (Molecular Beam Epitaxy) or LP-MOVPE (low pressure-metalorganic vapour phase epitaxy) technique. In this article the technological parameters and characterization of epilayers with small nitrogen content obtained by AP-MOVPE are presented. Under our growth conditions we achieve GaAs1-xNx/GaAs heterostructures which can be used for photodetector applications. We have focused our research on optical, electrical and structural properties of these material.