MOCVD Quantum Dots Cells Profile

The research team “MOCVD technology” is engaged in developing epitaxial technologies for growing in wide range of AIIIBV semiconductor materials by the MOCVD technique and also in developing and designing different PVC structures. The range of tasks being solved by the team includes the following main developments:

  • technology for growing semiconductor compounds and solid solutions in the arsenide system Al-Ga-In-As for creating different semiconductor devices;

  • technology for growing semiconductor compounds and solid solutions in the phosphide system Al-Ga-In-P for different applications;

  • technology for growing AIIIBV semiconductor compounds on alien substrates (Ge, Si);

  • approaches for investigating the growth process and for controlling PVC structure parameters by the optical in-situ methods including the reflectometry and anisotropic reflection spectroscopy methods;

  • epitaxial technologies for pseudo-amorphous growth on GaAs and Ge substrates and also investigation, calculation and development of single- and multi-junction PVC structures optimized for converting the direct and concentrated sunlight of the standard (AMO and AM1.5) and nonstandard spectral composition;

  • epitaxial technologies for growing lattice mismatched relaxed superlattices and their use in the technology for creating metamorphous and single- and multi-junction PVCs;

  • epitaxial technologies for growth and also investigation, calculation and development of structures of ~ 1µm laser radiation PVCs and receivers;

  • epitaxial technologies of growth and design of structures for autonomous power supply solar installations with solar spectrum splitting;

  • analytical procedures for calculating and approximating I-V and PV characteristics of different PVCs, investigation of fundamental intrinsic losses affecting their utilitarian characteristics;

  • controlled modes of thermal treating of different systems of metallic contacts of semiconductor devices manufactured on the base of developed epitaxial structures;

  • technologies for growing quantum-dimensional structures (quantum dots, quantum wells) in the In-Ga-As material system by the MOCVD technique and also technologies for compensating stresses in such structures;

  • technology and design of single- and multi-junction PVC structures based on materials with an intermediate band.

 

To create semiconductor device structures, the MOCVD technique is applied. The major instrument is the technological complex created on the basis of a R&D laboratory type MOCVD installation AIX200/4 (Fig.1a) with a horizontal quartz reactor (Fig.1b), in which gas-dynamics of laminar fluxes is realized.

The installation gas scheme (Fig.2) consists of the following sources. Sources of the III group elements - trimethylgallium, trimethylaluminum and trimethylindium; sources of the V group elements - arsine and phosphine, sources of p- and n-impurity atoms - diethylzinc and silane. Hydrogen is a gas-carrier. Such a configuration of the sources is allows growing wide range solid solutions used in heterostructures of different type PVCs.

 

For testing gown epitaxial layers and structures, a set of methods available in the Ioffe Institute is applied. For this reason, the MOCVD research team works in close cooperation with other teams and laboratories of the Institute. The following methods can be set off among the applied ones: X-ray diffractometry (XRD), scanning electronic microscopy (SEM), atom-force- microscopy (AFM), time-of-flight secondary-ionic mass-spectrometry (SIMS), Raman spectroscopy (RS), a number of methods for measuring electrical and physical layer parameters (charge carrier mobility, free charge carrier concentration and other). The testing methods are directed to elucidating the interrelation between growth conditions and material structural-optical characteristics.

Besides, the AIX200/4 installation is equipped with an EpiRAS2000T- in-situ measuring system (LayTec, Germany) (Fig.4) with a feasibility to measure: normalized reflection – reflectometry, reflection anisotropy – ellipsometry or spectrometry of reflection anisotropy (RAS) and real substrate temperature – pyrometry. This allows additionally controlling and determining during growth: thickness of grown epitaxial layers and structures, composition of multi-component solid solutions, doping level and type, surface stoichiometry and hetero-interface quality.

 

Besides, the research team is integrated into the process of fabricating PVCs based on grown heterostructures, in particular, in elaborating controllable modes of thermal treatment of different systems of metallic contacts deposited on semiconductor devices. The main instrument for developing technology is the SRO-702 installation (ATV Technology, Germany) (Fig.3).

 

Optimization of the design of different type PVCs being developed is carried out on the basis of analyzing spectral and I-V characteristics. For this purpose, also original analytical procedures are being elaborated, which allow establishing interrelation of growth conditions and electrical-optical characteristics of single- and multi-junction PVCs and determining fundamental losses arising during conversion of light into electric power. In a general case, a multijunction PVC constitutes (in the simplest case) subcells (single-junction SCs) connected in series by, for example, tunneling diodes. The number of diodes connected in parallel in the PVC equivalent circuit on each portion of their chain will depend on the number of current flow mechanisms in each p-n junction and are described by the diode parameters of the number of up to 16 (pre-exponential factors J0 and non-ideality factors A). For this reason, analytical description of I-V characteristics and PV dependencies in such a system is a rather difficult problem, which requires application of either numerical approaches or piecewise linear analytical description of separate portions of a MJ PVC I-V characteristic (Fig.5a). With using the analytical methods, one can approximate quite accurately the experimental I-V characteristics and PV dependencies of created MJ PVCs (Fig.5b).

 

The following can be related to the important activity steps of the MOCVD research team:

  • In 2004 – 2005 the technological complex on the base of the AIX200/4 MOCVD R&D installation was started up. The Russian laws in area of safety and the requirements imposed by the AIXTRON firm on providing the installation with gases, water and exhaust ventilation were complied. During preparation of the installation for starting up, all systems were created, tested and introduced into operation.

  • In 2007 work on creating the first in Russia MJ PVCs (dual-junction GaInP/GaAs PVCs) being a result of a whole number of developments and investigations was completed. In that number elaborated were original approaches to application of in-situ optical methods for controlling growth modes and determining epitaxial parameters of layers at experimental optimization of MJ heterostructures. Successful creation of the dual-junction wide-band GaInP/GaAs PVC grown on a GaAs substrate has allowed transferring the developed structure on the Ge substrate with simultaneous formation in it the additional third p-n junction.

  • MOCVD technology for triple-junction PVCs elaborated in the team has passed adaptation for the industrial epitaxial AIX2600G3 reactor and has been introduced into production on the enterprise “Saturn” (Krasnodar), where output of PVCs for space application was started in 2011-2012.

  • During 2012-2013 structures for fabricating receivers-converters of laser radiation were calculated, developed and optimized resulted in fabricating devices with the 60% efficiency.

  • From 2013 till now, development of technology of quantum-dimensional structures (quantum dots) and search for approaches to apply them in PVC heterostructures is carried out.