Microwave reflectivity from 4H-SiC under a high-injection condition: impacts of electron–hole scattering

Kato, Masashi; Mori, Yojiro; Ichimura, M.

doi:10.7567/jjap.54.04dp14

Cited by 13 publications

(12 citation statements)

References 35 publications

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“…The μ-PCD decay curves became gentle at high excitation density due to unproportionality of the microwave reflectivity to the excess carrier concentration such that Equation (3) would lose its validity 13,25,26 and τ 1/e would be overestimated. Moreover, time resolution depends on the performance of the measurement apparatus such as an excitation source, an oscilloscope, and an amplifier.…”

Section: Discussionmentioning

confidence: 99%

“…Among these techniques, µ-PCD is the most widely employed because compared to the other two as it exhibits surface roughness insensitivity (i.e., measurable for any given various surface roughness 8,9,10 ) and high signal sensitivity for excited carriers (i.e., using an optimum microwave component). In general, µ-PCD has been preferred for carrier lifetime measurement in SiC and other semiconductor materials 2,5,6,11,12,13,14,15,16,17,18,19 .…”

Section: Introductionmentioning

confidence: 99%

“…m-PCD also shows nonlinearity at a high injection condition, and overestimates carrier lifetime 13,25,26 . Figure 8 shows the measured m-PCD under a high excitation condition.…”

mentioning

confidence: 98%

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Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method

Asada

Ichikawa

Kato

2019

JoVE

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This work presents a protocol employing the microwave photoconductivity decay (μ-PCD) for measurement of the carrier lifetime in semiconductor materials, especially SiC. In principle, excess carriers in the semiconductor generated via excitation recombine with time and, subsequently, return to the equilibrium state. The time constant of this recombination is known as the carrier lifetime, an important parameter in semiconductor materials and devices that requires a noncontact and nondestructive measurement ideally achieved by the μ-PCD. During irradiation of a sample, a part of the microwave is reflected by the semiconductor sample. Microwave reflectance depends on the sample conductivity, which is attributed to the carriers. Therefore, the time decay of excess carriers can be observed through detection of the reflected microwave intensity, whose decay curve can be analyzed for estimation of the carrier lifetime. Results confirm the suitability of the μ-PCD protocol in measuring the carrier lifetime in semiconductor materials and devices.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method

Asada

Ichikawa

Kato

2019

JoVE

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“…17 In the measurements, the samples were immersed into a quartz cell filled with an aqueous solution or held in air ambient as a reference condition. For the aqueous solutions, we employed H 2 SO 4 , HCl, Na 2 SO 4 and NaOH with concentration of 1 mM to 1 M corresponding to pH range of the solution from 0 to 14.…”

Section: Methodsmentioning

confidence: 99%

Passivation of Surface Recombination at the Si-Face of 4H-SiC by Acidic Solutions

Ichikawa

Ichimura

Kimoto

et al. 2018

ECS J. Solid State Sci. Technol.

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We carried out carrier lifetime measurements for 4H-SiC single crystals in aqueous solutions with various pH by the microwave photoconductivity decay method. For both n-and p-type 4H-SiC, carrier lifetimes measured by Si-face excitation were longer in acidic aqueous solutions compared with carrier lifetimes measured in other solutions. On the other hand, for C-face excitation, carrier lifetimes did not depend on immersion solutions. These results indicate that carrier recombination centers at the surface of the Si-face was passivated by hydrogen ions. We also estimated surface recombination velocities Ss by a numerical analysis. S of the Si-face was reduced from 700 cm/s (in Na Silicon carbide (SiC) has attracted attention for high-power, highfrequency and high-temperature electronic devices due to its superior electrical and physical properties.1 In particular, bipolar devices based on 4H-SiC single crystals are operable in higher voltage ranges than conventional Si devices and thus development of bipolar devices is highly expected. Furthermore, SiC is applicable as photocathode for solar-to-hydrogen energy conversion. 2,3 In these applications, a carrier lifetime is an essential parameter for optimum design of the devices.1,2 So far, a point defect called the Z 1/2 center in n-type 4H-SiC single crystals has been identified as a dominant carrier recombination center.4-6 On the other hand, the carrier lifetime depends on surface recombination as well as bulk recombination induced by point defects and dislocations. Therefore, understanding of surface recombination is important for controlling the carrier lifetime and the surface recombination velocities Ss have been estimated for the Si-and C-faces of 4H-SiC.6-10 However, passivation methods for surface recombination on SiC have been rarely reported. In the case of Si, formation of surface oxide layers or immersion into HF suppress surface recombination and they have been utilized in practical applications. 11-13For 4H-SiC, although formation of high quality oxide layers is applicable to suppress surface recombination, 14,15 processes to form such layers are relatively complicated. In addition, SiC with insulating oxide layers cannot operate as photocathodes. Therefore, other methods to passivate SiC surfaces are required and, to establish passivation methods, we need to understand physics and chemistry for surface recombination phenomenon. In this report, we focus on passivation of surfaces of 4H-SiC single crystals by aqueous solutions. We measured carrier lifetime for 4H-SiC in various aqueous solution and discussed effects of the solutions on the surface condition. ExperimentalSamples used in this work were freestanding n-and p-type 4H-SiC epilayers which were originally grown with ∼150 μm thick on the (0001) Si-face with 4• woff angle toward <11 20> of bulk single crystal 4H-SiC substrates and then the substrates were completely polished. The n-type samples have a nitrogen donor concentration of 1 × 10 15 cm −3 , while the p-type samples have an aluminum ac...

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“…Carrier lifetime is a crucial parameter for 4H-SiC bipolar devices, thus many works are devoted to its investigation in epitaxial layers [1][2][3][4][5][6][7]. However, the injection level, temperature and defects lead to a wide variation of measured lifetimes.…”

Section: Introductionmentioning

confidence: 99%

Recombination and diffusion processes in electronic grade 4H silicon carbide

Ščajev¹,

Subačius²,

Jarašiūnas³

et al. 2019

physics

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Carrier dynamics in n-type 4H-SiC epilayers of varying thicknesses and low Z1/2 defect concentrations are investigated here in wide ranges of excess carrier density and temperature. Several techniques are employed to monitor carrier diffusion and recombination processes, including light induced transient grating (LITG), microwave photoconductance decay (MPCD) and free carrier absorption (FCA) using ps-laser pulses at 355 nm. The observed increase of the diffusion coefficient with the increasing excitation level is explained by the transition from the minority to the bipolar transport regime. Its subsequent decrease with even higher excitations is found to be governed by band-gap renormalization and degeneracy effects. The bulk lifetime, limited by hole traps at 0.19–0.24 eV above the valence band at lower excitations, was found to decrease from few microseconds to hundreds of nanoseconds during the transition regime from the minority to the bipolar transport. Our temperature-dependent measurements confirmed the trap activation energy and provided the approximate functional form of electron and hole lifetimes as τe = 340 × (T/300 K)3/2 ns and τh = 100 × (T/300 K)–1/2 ns, for the temperature T range 80–800 K. It was found to hold for 65 and 120 μm sample thicknesses, while the lifetimes were found to be twice shorter for the sample 35 μm thick.

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Microwave reflectivity from 4H-SiC under a high-injection condition: impacts of electron–hole scattering

Cited by 13 publications

References 35 publications

Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method

Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method

Passivation of Surface Recombination at the Si-Face of 4H-SiC by Acidic Solutions

Recombination and diffusion processes in electronic grade 4H silicon carbide

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