Growth and properties of compound semiconductors on germanium substrate

The aim of this thesis is to investigate the growth and characterisation of compound semiconductors on germanium (Ge) substrates. Also properties of detector applications and novel Ga(In)NAs compounds are presented on Ge substrates. The epitaxial growth is performed using metalorganic vapour phase epitaxy (MOVPE) technique. The nucleation of zinc blende lattice compound semiconductors on the surface of diamond lattice Ge are highly affected by different growth conditions such as temperature, growth rate and partial pressure of source materials. Thus, thorough characterisation of the fabricated structures and optimisation of the growth parameters are required. Three-dimensional island formation was observed for initial growth phases of GaAs and In(Ga)As on Ge. The properties of the self-assembled islands were investigated using atomic force microscopy (AFM). In0.5Ga0.5As islands grown at low temperature of 550° C showed a high areal density of 3.5 × 1010 cm−2 and uniformity in size. For grown GaAs layers the high initial island density and uniformity enables homogeneous coalescence of the islands as the growth is continued and results in smooth two-dimensional GaAs surfaces already at small layer thicknesses. The crystal and optical properties of GaAs and Ga(In)NAs layers were investigated using high resolution X-ray diffraction (HRXRD), synchrotron X-ray topography (SXT) and photoluminescence (PL). In SXT measurements a 650 nm thick GaAs layer grown on Ge showed very small dislocation density of 250–500 cm−2. The value is better than was found by SXT for the vapour pressure controlled Czochralski (VCz) grown GaAs substrates. The growth of GaAs on misoriented Ge substrate results in a tilt angle between the lattice planes of the substrate and the layer. For these structures it was shown that a specific HRXRD setup, in which the diffraction plane is parallel with the step edges on the Ge surface, enables accurate measurements and analyses of the structures. From a GaInNAs multi-quantum well structure on Ge photoluminescence at telecommunication wavelength of 1.55 µm was obtained. From the HRXRD and PL results a nitrogen incorporation of about 5 % was determined for the quantum wells. Also for a GaAs/Ge matrix detector structure a record low leakage current of 3 × 10−9 A/cm2 was obtained at 77 K. From arsenic diffusion based matrix detector fabricated on Ge substrate an excellent resolution of 220 eV at 5.9 keV and 400 eV at 60 keV was measured.

Department dc:contributor.department

Department of Electrical and Communications Engineering

Grantor dc:publisher

Helsinki University of Technology

Year dc:date.issued

2006

Author dc:creator

• Knuuttila, Lauri

Contributors dc:contributor

• Aalto-yliopisto
• Aalto University

Language dc:language.iso

en

Repository record dc:identifier.uri

https://aaltodoc.aalto.fi/handle/123456789/2694

OAI record oai:identifier

https://aaltodoc.aalto.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Aaaltodoc.aalto.fi%3A123456789%2F2694