Study of nonlinear optical effects in GaN:Mg epitaxial film

Zhang, H. Y.; He, X. H.; Shih, Yanhua; Schurman, M.; Feng, Zhe; Stall, R. A.

doi:10.1063/1.117741

Cited by 62 publications

(37 citation statements)

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“…It is interesting to note that the oscillation is cosinusoidal, indicating a displacive initiation mechanism. With a 390-nm wavelength and a refractive index of 2.6 in GaN [67], the pump longitudinal self-interference spacing is 75 nm, which is half the UV pump wavelength inside the sample. For this particular interference pattern, an oscillation frequency of 106 GHz was observed.…”

Section: Generation Of Coherent La Phonons In Strained Gan Thin Filmsmentioning

confidence: 99%

Generation of Coherent Acoustic Phonons in Nitride-Based Semiconductor Nanostructures

Chern

Sun

Sanders

et al. 2004

Topics in Applied Physics

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Abstract. In this chapter, we review experimental and theoretical aspects of coherent acoustic phonon generation in nitride-based semiconductor nanostructures, with particular application to InGaN/GaN multiquantum wells (MQWs). We first discuss the experimental generation and detection of coherent longitudinal-acoustic (LA) phonon oscillations in InGaN/GaN MQWs using the transmission-type pump-probe technique. With UV femtosecond pulse excitation, photogenerated carriers screen the piezoelectric field and initiate the displacive coherent phonon oscillations. The spatial wavevector of the periodic carrier distribution determines the phonon-oscillation frequency. The induced acoustic phonon oscillations result in a piezoelectric field modulation that then causes an absorption variation through the Franz-Keldysh effect. Injecting another control pulse can further control the resulting coherent phonon oscillations. Both magnitude and phase manipulation can be achieved by controlling the intensity and time delay of the control pulse. After reviewing the experimental results, we then present a microscopic theory of the generation and propagation of coherent LA phonons in wurtzite semiconductor MQWs. Under typical experimental conditions, the propagation of coherent LA phonons is described by a loaded-string equation for the lattice displacement, where the timeand position-dependent loading term is a function of the photoexcited carrier density. We note that this differs from the situation in which coherent LO-phonon scillations are generated in bulk systems where the coherent LO phonons obey a forced-oscillator equation as opposed to a loaded-string equation. Both deformation-potential and piezoelectric-coupling mechanisms contribute to the driving force in the loaded-string equation. We also discuss a macroscopic theory for the generation and dynamics of coherent acoustic phonons in wurtzite semiconductor nanostructures. This approach is based on macroscopic continuum constitution equations for piezoelectric wurtzite semiconductors. Starting from Poisson's equation and the dynamic elastic equation, a vector-loaded wave equation is obtained. By projecting the corresponding equation to eigenvectors of the elastic Christoffel equation, the loaded-string equation can also be obtained. The macroscopic approach is then used to study the orientation effects on the generation of coherent acoustic phonons and it is found that large coherent transverse acoustic phonon oscillation can be generated when the growth direction of the nanostructure is along Kong-Thon Tsen (Ed.): Ultrafast

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Section: Generation Of Coherent La Phonons In Strained Gan Thin Filmsmentioning

confidence: 99%

Generation of Coherent Acoustic Phonons in Nitride-Based Semiconductor Nanostructures

Chern

Sun

Sanders

et al. 2004

Topics in Applied Physics

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“…2(b) and the oscillation frequency is 115 GHz. The refractive index of GaN at 373 nm is 2.6 [14]. From Eq.…”

Section: Setupmentioning

confidence: 98%

Generation of coherent acoustic phonons in GaN‐based p‐n junction

Lin

Keller

et al. 2004

phys. stat. sol. (c)

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PACS 62.30.+d, 78.20.Hp Coherent acoustic phonons were generated in the piezoelectric bulk semiconductor through inverse piezoelectric effect by femtosecond laser pulses. While the photocarriers are generated in the depletion region of the piezoelectric semiconductor, the electrons and holes sweep in counter-directions due to the built-in electric field and result in strain pulses through the piezoelectric effect. 1 Introduction Piezoelectric effect has been utilized to generate acoustic waves for a long time. The typical method to generate and detect acoustic wave is to apply and monitor the electric bias changes of electrodes on a piezoelectric material. However, current methods have limitations for the adoption of higher acoustic frequency due to the difficulty to shorten the interval of electrodes and the bandwidth limitation of the electronic system.Optoacoustic conversion provides a way to induce acoustic pulses with frequencies in GHz to THz range. Several mechanisms of optoacoustic conversion include thermoelastic effect, deformation coupling, piezoelectric effect, and light pressure were theoretically analysed in Ref. 1. Experimentally, picosecond (ps) ultrasonics has demonstrated to generate acoustic pulses with pulsewidth of several picoseconds through thermoeleastic effect or deformation coupling [2].Gusev proposed a theoretical model and showed that the conversion efficiency of inverse piezoeffect mechanism is more efficient than thermoelastic effect and deformation coupling to optically excite ps acoustic pulses in piezoelectric semiconductors [3]. Laser-induced piezoexcitation of shear bulk acoustic pulses [4] and surface acoustic waves [5] were experimentally demonstrated, however, the pulsewidth was on the order of several hundred nanoseconds. Recently, we observed large THz coherent acoustic phonon oscillation in GaN based heterostructure due to the screening of the photoexcited carriers in the strain-induced built-in piezoelectric field [6,7]. Theoretical analysis reveals that the piezoelectric coupling mechanism is the dominated term [8,9].Besides the generation of coherent acoustic phonons in the strain-induced piezoelectric field [6][7][8][9], in this paper, we demonstrate the generation of acoustic pulses with pulsewidth on the order of 10 ps in the GaN homostructure through inverse piezoelectric effect by optically injecting free carriers in the p-n junction. Due to the built-in electric field in the depletion region, the electrons and holes sweep in counter-directions and result in the variation of electric field. Since the characteristics of the acoustic

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“…AMATSU R-928) placed behind interference optical filters centered at 355 ± 5 nm. The THG-device was previously calibrated by means of a fused silica plate (v (3) % 3.11 · 10 À14 esu, at k x = 1064 nm), which is frequently used as a NLO-reference standard via the Maker-Fringes method [1,3,5,[44][45][46][47].…”

Section: Linear and Nonlinear Optical Characterizationmentioning

confidence: 99%