Ultrafast hot electron relaxation time anomaly in InN epitaxial films

Tsai, Tsong-Ru; Chang, Chih-Fu; Gwo, Shangjr

doi:10.1063/1.2751110

Cited by 37 publications

(37 citation statements)

References 26 publications

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“…This thermalization slows at high fluence [ Fig. 6(a)], in keeping with many, [28][29][30] but not all, 31 prior observations. The slowing is attributed to the hot-phonon effect: 32 hot electrons couple primarily to LO phonons.…”

supporting

confidence: 58%

Diffusion of degenerate minority carriers in a p-type semiconductor

Weber

Kittlaus

2013

Journal of Applied Physics

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We report ultrafast transient-grating experiments on heavily p-type InP at 15 K. Our measurement reveals the dynamics and diffusion of photoexcited electrons and holes as a function of their density n in the range 2 × 10 16 to 6 × 10 17 cm −3 . After the first few picoseconds the grating decays primarily due to ambipolar diffusion. While at low density we observe a regime in which the ambipolar diffusion is electron-dominated and increases rapidly with n, at high n it appears to saturate at 34 cm 2 /s. We present a simple calculation that reproduces the main results of our measurements as well as of previously published measurements that had shown diffusion to be a flat or decreasing function of n. By accounting for effect of density on charge susceptibility we show that, in p-type semiconductors, the regime we observe of increasing ambipolar diffusion is unique to heavy doping and low temperature, where both the holes and electrons are degenerate; in this regime the electronic and ambipolar diffusion are nearly equal. The saturation is identified as a crossover to ambipolar diffusion dominated by the majority carriers, the holes. At short times the transient-grating signal rises gradually. This rise reveals cooling of hot electrons and, at high photocarrier density, allows us to measure ambipolar diffusion of 110 cm 2 /s in the hot-carrier regime.

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supporting

confidence: 58%

Diffusion of degenerate minority carriers in a p-type semiconductor

Weber

Kittlaus

2013

Journal of Applied Physics

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“…Figure 4 shows the detected differential probe signal versus the pump-probe time delay for both samples. For the InN sample, the measured decay cannot be well fitted with a single-exponential function, as already observed by other authors, [17][18][19] revealing the coexistence of various carrier relaxation paths. In order to investigate the origin of these different processes, power-dependent measurements were performed, showing that the initial relaxation time constant decreases from 30 to 13 ps when the excitation carrier density increases from n exc % 4.3 Â 10 18 to 3.8 Â 10 19 cm À3 (inset of Fig.…”

Section: à3mentioning

confidence: 88%

“…20 The solid line in the inset of Fig. 4 17 pumping at 780 nm (1.59 eV). The second nonradiative relaxation mechanism, associated to the slower decay occurring at longer delays (s $ 70 6 7 ps, consistent with the obtained value of A defect ), is attributed to the recombination of the carriers via defects in the structure.…”

Section: à3mentioning

confidence: 99%

Carrier localization in InN/InGaN multiple-quantum wells with high In-content

et al. 2012

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We study the carrier localization in InN/In 0.9 Ga 0.1 N multiple-quantum-wells (MQWs) and bulk InN by means of temperature-dependent photoluminescence and pump-probe measurements at 1.55 lm. The S-shaped thermal evolution of the emission energy of the InN film is attributed to carrier localization at structural defects with an average localization energy of $12 meV. Carrier localization is enhanced in the MQWs due to well/barrier thickness and ternary alloy composition fluctuations, leading to a localization energy above 35 meV and longer carrier relaxation time. As a result, the luminescence efficiency in the MQWs is improved by a factor of five over bulk InN. The extension of the operation wavelength of III-nitrides to the near-infrared (NIR) range is possible thanks to the growth of high-quality InN films displaying a bandgap energy close to 0.65 eV (1.9 lm) at room temperature (RT). The particular optical and electronic properties of this semiconductor have rendered it a subject of extensive research aimed at the development of devices for photovoltaics, optoelectronics (laser diodes and detectors), highspeed electronics, opto-chemical sensing, and terahertz applications.1 Furthermore, thanks to the close-to-resonant behavior at 1.5 lm and saturable absorption of InN with recovery times in the picosecond range, 2 this semiconductor has emerged as a promising choice for all-optical signal processing applications in optical communication networks.From this point of view, low-dimensional InN-based structures such as multi-quantum-wells (MQWs) 3-5 or quantum dots (QDs) 6,7 can improve the efficiency of NIR devices by tuning their operation wavelength through bandgap engineering. Furthermore, the improved carrier confinement should lead to an enhanced linear and nonlinear optical response at resonant wavelengths. In this sense, strong absorption saturation has been recently demonstrated in high-In content InN/InGaN MQWs at 1.55 lm.8 In this paper, we investigate the carrier localization in InN/InGaN MQW structures by means of temperature-dependent photoluminescence (PL) measurements and pump-probe spectroscopy at 1.55 lm. Our results show that a fivefold increase in luminescence efficiency can be obtained in these nanostructures compared to bulk InN. This is consistent with the observation of a longer carrier lifetime in the MQW structure over the bulk material.The samples under study were grown by plasma-assisted molecular-beam epitaxy (PAMBE) on 10-lm-thick GaN-onsapphire templates. The substrate temperature during growth was 450 C and the N-limited growth rate was fixed at 280 nm/h. The MQW structure, designed to have a quasiresonant interband transition at 1.55 lm, consists of 41 periods of InN/In 0.9 Ga 0.1 N QWs with well and barrier thickness of 4.5 nm and 7 nm, respectively. The growth of the MQW structure starts with an InN layer (4.5 nm) at the substrate/ MQW interface, which assures the relaxation of at least 90% of the lattice mismatch at the first interface, as verified in situ by reflective high-en...

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“…In particular, femtosecond IR pulses have been widely employed in ultrafast spectroscopy to investigate the carrier dynamics in semiconductor structures using pump-probe measurements [120][121][122]. Due to the wavelength tunability of chirp manipulated OPA accompanied with the ultrashort pulse duration, the generated pulses with lower photon energy compared to Ti:sapphire laser can be helpful in probing the carrier relaxation process.…”

Section: Prospects and Conclusionmentioning

confidence: 99%

Ultrafast Mid-IR Laser Pulses Generation via Chirp Manipulated Optical Parametric Amplification

et al. 2018

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Abstract:Over the past decades, optical parametric amplification (OPA) has become one of the most promising sources of ultrafast Mid-IR laser, owing to its outstanding properties including ultrabroad bandwidth, superior tunability, good beam quality, and scalable energy. In this paper, we review the recent progress in ultrashort laser pulse generation via chirp manipulated OPA, which improves the energy scalability and gain bandwidth by strategically chirping both pump and seed pulses. The gain mechanism is theoretically analyzed and the OPA processes are numerically simulated. In addition, the concept is verified experimentally. Femtosecond pulses with hundreds of mJ are generated in a high energy dual-chirped-OPA (DC-OPA), and ultrabroadband µJ-level spectra supporting sub-2-cycle pulse durations are achieved in BBP-OPA. Furthermore, the obtained pulses show excellent tunability through the NIR to Mid-IR regions, which makes them a suitable seeding source for further amplification as well as powerful tools in various applications such as strong field physics, attosecond science, and ultrafast spectroscopy.

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Ultrafast hot electron relaxation time anomaly in InN epitaxial films

Cited by 37 publications

References 26 publications

Diffusion of degenerate minority carriers in a p-type semiconductor

Diffusion of degenerate minority carriers in a p-type semiconductor

Carrier localization in InN/InGaN multiple-quantum wells with high In-content

Ultrafast Mid-IR Laser Pulses Generation via Chirp Manipulated Optical Parametric Amplification

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