Mateusz Wośko

Stress engineering in GaN structures grown on Si(111) substrates by SiN masking layer application

GaN layers without and with an in-situ SiN mask were grown by using metal organic vapor phase epitaxy for three different approaches used in GaN on silicon(111) growth, and the physical and optical properties of the GaN layers were studied. For each approach applied, GaN layers of 1.4 μm total thickness were grown, using silan SiH4 as Si source in order to grow SixNx masking layer. The optical micrographs, scanning electron microscope images, and atomic force microscope images of the grown samples revealed cracks for samples without SiN mask, and micropits, which were characteristic for the samples grown with SiN mask. In situ reflectance signal traces were studied showing a decrease of layer coalescence time and higher degree of 3D growth mode for samples with SiN masking layer. Stress measurements were conducted by two methods—by recording micro-Raman spectra and ex-situ curvature radius measurement—additionally PLs spectra were obtained revealing blueshift of PL peak positions with increasing stress. T...

Fabrication of ohmic contact based on platinum to p-type compositionally graded AlGaAs layers

Novel metallization scheme was proposed for ohmic contact formation to compositionally graded p-type AlGaAs. A metal multilayers of Ti/Pt/Au, Pt/Ti/Pt/Au and Pt/Ti/Ni/Au were deposited by thermal evaporation using electron gun and resistance heater. The contacts were sequentially annealed by rapid thermall annealing system in N2 atmosphere at various temperatures (in the range from 350°C to 550°C). The duration of annealing step was 2 minutes. The as-deposited Pt/Ti/Pt/Au and Pt/Ti/Ni/Au multilayer metallizations had resistivities of 1.4·10-5 Ω·cm2 which have been gradually deteriorated after each subsequent annealing. The current-voltage characteristics of the ohmic contacts to compositionally graded p-type AlGaAs epitaxial layers were studied and discussed.

Surface topography analysis with application of roughness area dependence method.

At the moment the root mean square roughness (Rq) is the most commonly used parameter for quantitative description of surface properties. However, this parameter has one main disadvantage: for its calculation only height variations of surface profile are used which are then represented by a single number. To eliminate this restriction authors of the paper have developed a surface analysis method which is based on roughness calculation in the function of gradually increasing dimensions of a sampling area. By setting proper measurement parameters and further data processing, from Rq dependence on sampling area plot size there is a possibility to obtain more useful, additional information about specific surface properties than using the single roughness value. Roughness area dependence plots, obtained from AFM images, were analyzed to study the influence of different growth parameters on surface properties of GaN layers and AlGaN/GaN heterostructures grown on sapphire and silicon substrates by Metal Organic Chemical Vapor Deposition (MOVPE) epitaxy. Although the method was used to characterize the semiconductor material in micrometer range, it can be applied also for any topography imaging technique in wide scale ranges.

Origin of surface defects and influence of an in situ deposited SiN nanomask on the properties of strained AlGaN/GaN heterostructures grown on Si(111) using metal–organic vapour phase epitaxy

Herein, the investigation of the defects present on the surface of strained AlGaN/GaN heterostructures grown on Si(111), with and without an in situ deposited SixNx nanomask, was carried out. The SiN nanomask was used to enable the growth of dislocation and biaxial stress reduced AlGaN/GaN/Si(111) HEMT-type structures by the metal–organic vapor phase epitaxy (MOVPE) method. Specifically, the growth process model was proposed for the MOVPE deposition of a GaN layer on SiN/AlN/Si(111) templates, which includes the defects observed using scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Moreover, X-ray diffraction, photoluminescence and microRaman methods were used to characterize and compare the structural and optical properties of the strained AlGaN/GaN HEMT-type structures grown with and without application of the in situ SixNx nanomask. It was observed that the SiN deposition on top of the HT-AlN, prior to the GaN growth, has substantial effects on the properties of the final AlGaN/GaN heterostructure, such as the biaxial state of stress, threading dislocation density and crystal quality. The influence of the observable defects is discussed, along with their predicted influences on the essential properties of the device structure.

Correlation of Selected Problems During Gan Movpe Epitaxy on si Substrates with in–Situ Interferometer Observation

Abstract In this paper, selected problems occurring during GaN epitaxy on Si substrates are correlated with in-situ interferometer observations based on structures fabricated using 3×2” Thomas Swan Close Coupled Showerhead MOVPE system. Samples were epitaxially grown on highly resistive (> 500cm) p-type 2” silicon substrates. The growth was observed using an interferometer acquiring reflectance traces in-situ. To avoid issues that are shown in this paper, different approaches of the so-called buffer layer were used by depositing them on Si before the growth of GaN. Different material qualities of grown GaN layers were obtained by variation in films constituting the buffer layer grown before the desirable GaN film. The study shows the evolution of the grown samples, improvement of various parameters and also gradual reduction of material issues discussed in this paper. Improvement in GaN layer was mainly observed by SEM characterization and studying the growth mechanisms through observation of reflectance traces obtained in-situ.

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.

Evaluation of AlGaN/GaN heterostructures properties by QMSA and AFM techniques

Atomic force microscopy and Quantitative Mobility Spectrum Analysis (QMSA) were applied for characterization and evaluation of the quality of AlGaN/GaN heterostructures. The structural uniformity, growth mode and electrical properties of the heterostructures were determined. The obtained results indicated that the time of growth of the low temperature GaN nucleation layer influenced the morphology and electrical properties of the AlGaN/GaN heterostructure.

The influence of MOVPE process parameters on the buffer resistivity used in AlGaN/GaN heterostructures

The influence of growth conditions on properties of high temperature GaN (HT-GaN) buffer used in AlGaN/GaN HEMT heterostructures was studied. Many various factors are presumed to have significant impact on the concluding properties of HT-GaN buffer. In this paper the nucleation layer growth time as well as temperature during high temperature GaN layer growth was selected as a factors alleged to cause variation in final GaN layer properties. The study was designed to show step by step improvement of HT-GaN buffer with consecutive changes of particular parameters. Electrical properties of the AlGaN/GaN heterostructures were determined using impedance spectroscopy method performed with HP 4192A impedance meter equipped in two contact mercury probe. Laser reflectance traces acquired in-situ during MOVPE (Metalorganic Vapor Phase Epitaxy) growth were compered and analyzed in order to correlate growth mechanism with electrical properties of HT-GaN buffer. The improvement of HT-GaN resistivity was shown through decrement of capacitance in the depleted space-charge region.

Growth and coalescence control of inclined c-axis polar and semipolar GaN multilayer structures grown on Si(111), Si(112), and Si(115) by metalorganic vapor phase epitaxy

Herein, silicon substrates in alternative orientations from the commonly used Si(111) were used to enable the growth of polar and semipolar GaN-based structures by the metalorganic vapor phase epitaxy method. Specifically, Si(112) and Si(115) substrates were used for the epitaxial growth of nitride multilayer structures, while the same layer schemes were also deposited on Si(111) for comparison purposes. Multiple approaches were studied to examine the influence of the seed layers and the growth process conditions upon the final properties of the GaN/Si(11x) templates. Scanning electron microscope images were acquired to examine the topography of the deposited samples. It was observed that the substrate orientation and the process conditions allow control to produce an isolated GaN block growth or a coalesced layer growth, resulting in inclined c-axis GaN structures under various forms. The angles of the GaN c-axis inclination were determined by x-ray diffraction measurements and compared with the results ...

Precise etching of AlGaN/GaN HEMT structures with Cl 2 /BCL 3 /Ar plasma

The aim of work was to develop precise etching process of AlGaN/GaN heterostructures. The study was focused on surface parameters evolution and etch characteristics of etched layers. The surface parameters depended on selection of composition of Cl₂:BCl₃:Ar gas mixture, while the amount of boron trichloride in Cl₂:BCl₃:Ar was crucial in obtaining precise etch rate of thin AlGaN and thick uid-GaN layers. Changing of BCl₃ amount in the Cl₂:BCl₃:Ar mixture in the range of 6% ÷ 60% resulted in increased AlGaN etch rate from 1 nm/min to 19 nm/min and uid-GaN etch rate from 11 nm/min to 55 nm/min. In case of AlGaN almost linear etch characteristic was observed. Surface morphology of uid-GaN was modified by different ratio of BCl₃/Cl₂.