Ramazan Atalay

The influence of substrate polarity on the structural quality of InN layers grown by high-pressure chemical vapor deposition

The influence of substrate polarity on the properties of InN layers grown by high-pressure chemical vapor deposition has been studied. The 2Θ-ω x-ray diffraction scans on InN layers deposited on polar GaN epilayers revealed single-phase InN(0002) with a full width at half maximum (FWHM) of around 200arcsec. InN layers grown on N-polar GaN exhibit larger FWHMs. Rocking curve analysis confirmed single-phase InN for both growth polarities, with FWHM values for ω-RC(002) at 2080arcsec for InN grown on Ga-polar templates. The A1(LO) Raman mode analysis shows higher free carrier concentrations in InN grown on N-polar templates, indicating that polarity affects the incorporation of impurities.

Optical characterization of InN layers grown by high-pressure chemical vapor deposition

The optical properties of InN layers grown by high-pressure chemical vapor deposition have been studied. Raman, infrared reflection, and transmission spectroscopy studies have been carried out to investigate the structural and optical properties of InN films grown on sapphire and GaN/sapphire templates. Results obtained from Raman and IR reflectance measurements are used to estimate the free carrier concentrations, which were found to be varying from mid 1018 to low 1020cm−3. The values for free carrier concentrations are compared to optical absorption edge estimates obtained from optical transmission spectra analysis. The analysis shows that optical absorption edge for InN shifts below 1.1eV as the free carrier concentration decreases to low 1018cm−3.

Growth temperature - phase stability relation in In 1-x Ga x N epilayers grown by high-pressure CVD

The influence of the growth temperature on the phase stability and composition of singlephase In 1-x Ga x N epilayers has been studied. The In 1-x Ga x N epilayers were grown by high-pressure Chemical Vapor Deposition with nominally composition of x = 0.6 at a reactor pressure of 15 bar at various growth temperatures. The layers were analyzed by x-ray diffraction, optical transmission spectroscopy, atomic force microscopy, and Raman spectroscopy. The results showed that a growth temperature of 925 °C led to the best single phase InGaN layers with the smoothest surface and smallest grain areas.

Effect of reactor pressure on the electrical and structural properties of InN epilayers grown by high-pressure chemical vapor deposition

The influence of super-atmospheric reactor pressures (2.5‐18.5bar) on the electrical and structural properties of InN epilayers deposited on GaN/sapphire (0001) templates by high-pressure chemical vapor deposition has been studied. The epilayers were analyzed by Raman, x-ray diffraction (XRD), and Fourier transform infrared reflectance spectrometry to determine the structural properties as well as the phonon frequencies, dielectric function, plasma frequency, layer thickness and damping parameters of the epilayers. For the studied process parameter space, best material properties were achieved at a reactor pressure of 12.5bar and a group-V/III ratio of 2500 with a free carrier concentration of 1.5 � 10 18 cm � 3 , a mobility of the bulk InN layer of 270 cm 2 V � 1 s � 1 , and a Raman (E2 high) FWHM value of 10.3cm � 1 . This study shows that the crystalline layer properties—probed by XRD 2h‐x scans—improve with increasing reactor pressure. V C 2012

Observation of NH2 species on tilted InN (011−1) facets

The structural properties and surface bonding configuration of InN layers grown by high-pressure chemical vapor deposition have been characterized using Raman spectroscopy, x-ray diffraction (XRD), and high resolution electron energy loss spectroscopy. The appearance of the A1(TO) mode at 447 cm−1 in unpolarized z(·)z− Raman spectrum indicates distortions in the crystal lattice due to the growth of tilted plane crystallites. A Bragg reflex in the x-ray diffraction spectrum at 2Θ ≈ 33° has been assigned to tilted InN facets in the polycrystalline InN layer. The high resolution electron energy loss spectrum for this InN layer features vibration modes assigned to NH2 species indicating a surface orientation consistent with the crystalline properties observed in Raman spectroscopy and XRD. The appearance of tilted planes is suggested to be due to the effects of high V–III ratio and lattice mismatch on the growth mechanism.

Reactor pressure - growth temperature relation for InN epilayers grown by high-pressure CVD

Results on the achievable growth temperature as a function of the reactor pressure for the growth of InN by high-pressure CVD are presented. As the reactor pressure was increased from 1 bar to 19 bar, the optimal growth temperature raised from 759°C to 876°C, an increase of 6.6 °C/bar. The InN layers were grown in a horizontal flow channel reactor, using a pulsed precursor injection scheme. The structural and optical properties of the epilayers have been investigated by Raman spectroscopy, X-ray diffraction, and IR reflectance spectroscopy.

Effect of V/III molar ratio on the structural and optical properties of InN epilayers grown by HPCVD

The dependency of the structural and optoelectronic properties of InN thin films grown by high-pressure chemical vapor deposition technique on the group V/III molar precursor ratio has been studied. X-ray diffraction, Raman spectroscopy, and IR reflectance spectroscopy have been utilized to study local- and long-range structural ordering as well as optoelectronic properties of the InN epilayers grown on crystalline sapphire substrates. The investigated InN epilayers were grown with group V/III molar precursor ratio varying from 900 to 3600, while all other growth parameters were kept constant. For a group V/III precursor ratio of 2400, the full width-half maximum of the Raman E2(high) mode and XRD (0002) Bragg reflex exhibit minimums of 7.53 cm⁻¹ and 210 arcsec, respectively, with maximized grain size and reduced in-plane strain effect. FTIR data analysis reveals a growth rate of 120 nm/hr, a carrier mobility of 1020 cm²V⁻¹s⁻¹, and a free carrier concentration of 1.7×1018 cm⁻³ for a V/III ratio of 2400. The Raman analysis indicate that non-polar E2(high) mode position remains unaffected from a changing V/III ratio; whereas, polar A1(LO) mode position significantly changes with changing V/III ratio. Optical analysis also suggests that LO-phonon correlates with free carrier concentration (ne) and TO-phonon correlates with free carrier mobility (μ) in the InN epilayers.

Effect of nucleation period on the physical properties of InN epilayers

The influence of structural and optoelectronic properties of InN epilayers on the duration of initial nucleation has been studied. High pressure chemical vapor deposition (HPCVD) has been utilized to deposit InN epilayers on GaN/sapphire (0001) templates at a reactor pressure of 15 bar. The initial nucleation period was varied between 10 s and 60 s, leaving all other growth parameters constant. The structural properties of the grown samples have been investigated by X-ray diffraction (XRD) spectroscopy and Raman spectroscopy. The optoelectronic properties were analyzed by Fourier transform infra-red (FTIR) spectroscopy. The layer thickness, free carrier concentration and void fraction were obtained by simulating IR spectra, using multi-layer stack model for epilayers and Lorentz-Drude model for dielectric function. Raman, X-ray diffraction (XRD) and void fraction calculation results suggest that the optimum nucleation time is between 10 - 20 s. However, simulation results revealed that the free carrier concentration of the bulk layer does not show any significant dependency on the duration of initial nucleation.