Terahertz time-domain ellipsometry with high precision for the evaluation of GaN crystals with carrier densities up to 1020 cm−3

Abstract

Gallium nitride (GaN) is one of the most technologically important semiconductors and a fundamental component in many optoelectronic and power devices. Low-resistivity GaN wafers are in demand and actively being developed to improve the performance of vertical GaN power devices necessary for high-voltage and high-frequency applications. For the development of GaN devices, nondestructive characterization of electrical properties particularly for carrier densities in the order of 1019 cm−3 or higher is highly favorable. In this study, we investigated GaN single crystals with different carrier densities of up to 1020 cm−3 using THz time-domain ellipsometry in reflection configuration. The p- and s-polarized THz waves reflected off the GaN samples are measured and then corrected based on the analysis of multiple waveforms measured with a rotating analyzer. We show that performing such analysis leads to a ten times higher precision than by merely measuring the polarization components. As a result, the carrier density and mobility parameters can be unambiguously determined even at high conductivities.

Ultrafast visualization of an electric field under the Lorentz transformation

“…The latter thus demands near-field ultrafast (subpicosecond) measurements. An application of electro-optic (EO) sampling [20][21][22][23] (Methods; often utilized in ultrafast terahertz spectroscopy [20][21][22][23][24][25][26][27][28] ) to relativistic electron beams began in 2000, and temporal evolution of the relativistic Coulomb field was obtained with high temporal resolution, with the LT of the electromagnetic potential implicitly assumed to be valid 29 . Here we present spatiotemporal images of the electric field around a relativistic electron beam, obtained by EO sampling.…”

Production of Single Crystalline Seeds of Organic Nonlinear Optical Materials via Laser Ablation

“…Crystal quality was assessed by THz wave measurement , and crossed Nicols imaging. The THz emission of the DAST crystals was measured at ambient room conditions (temperature = 22 ± 1 °C, relative humidity ∼25%) by utilizing each target DAST crystal as the THz emitter in an in-house built transmission-type THz time-domain spectrometer with a Ti:sapphire laser oscillator (Tsunami, Spectra-Physics, repetition rate: ∼80 MHz) as the source of pump and probe pulses (λ = 800 nm, Δ t = 100 fs).…”

360° Polarization Control of Terahertz Spintronic Emitters Using Uniaxial FeCo/TbCo2/FeCo Trilayers

“…In any case, the magnetic anisotropy controlled spintronic emitter opens as such an effective way to implement time domain ellipsometry at THz frequencies. This technique has during the past decade established itself as a powerful THz spectroscopic tool allowing to bypass the need for a measurement against a standard reference sample, having a larger spectral coverage than frequency domain spectroscopy, and providing direct access to phase information. , Of the remaining challenges to be solved, the quality of the THz polarizing optical component needed to obtain the ellipsometric functions is an important one . Using the here proposed emitter, a source with easily variable s- and p-polarization becomes available that is moreover intrinsically very broadband.…”

“…This technique has during the past decade established itself as a powerful THz spectroscopic tool allowing to bypass the need for a measurement against a standard reference sample, having a larger spectral coverage than frequency domain spectroscopy, and providing direct access to phase information. 57,58 Of the remaining challenges to be solved, the quality of the THz polarizing optical component needed to obtain the ellipsometric functions is an important one. 59 Using the here proposed emitter, a source with easily variable s-and ppolarization becomes available that is moreover intrinsically very broadband.…”