Pump and probe measurement of intersubband relaxation time in short-wavelength intersubband transition

Abstract

Population relaxation dynamics of the short-wavelength (∼2.5 μm) intersubband transition (ISB-T) in narrow InGaAs/AlAs quantum wells is investigated. Femtosecond (∼100 fs) pump and probe measurement yields a relaxation time of ∼2.7 ps, which is as fast as those observed for 10–5 μm ISB-T (0.7–1.5 ps, respectively). The ISB relaxation time increases more rapidly than that predicted from the usual intersubband optical-phonon scattering model as the ISB-T energy increases. Our theoretical calculation, which takes into account the intrasubband energy relaxation process, agrees well with the experimental results. The intrasubband energy relaxation process is found to be important in the short-wavelength region.

Short-wavelength (λ<2 μm) intersubband absorption dynamics in ZnSe/BeTe quantum wells

“…4͑b͒, the experimental decay times are compared with a calculation based on the Ridley's model. 7 The processes involved in the calculation are comprised of electron scatterings by a confined LO phonon emission from the bottom of e 2 subband to e 1 subband with a large in-plane momentum, and by cascaded emission of interface LO phonons down to the bottom of e 1 subband at 300 K. 7,11 The comparison with the experimental data indicates that the fast decay component comes from the intersubband relaxation process considered here. It should be noted that the fast relaxation times obtained here have a comparable value reported for a 1.75 m ISBT on GaN QW ͑0.37 ps͒.…”

III-V Detectors

“…Acoustic phonons are low energy vibrations of the semiconductor's unit-cells [111]. 3. the guided mode model [185,219] -both macroscopic calculations with differing boundary conditions for the vibrational amplitudes of phonon modes and for the electrostatic potental 4.…”

“…Key: n-mod = mod ulation doped with donor impurities, n-doped = sample was uniformly doped with donor impurities, T = the lattice temperature of the sample, FEL = free electron laser, PV = Photovoltage measurement, PL = Photoluminecence mea surement, CW = Continous Wave, VIS implies interband excitation, whilst IR implies intersubband excitation, MC = Monte-Carlo calculation performed using experimental data, At = pulse-width of laser pulse and /0 = intensity of laser. Time resolved pump-probe spectroscopy: Pump-probe absorption (trans mission) spectroscopy of semiconductor quantum-wells has been conducted using parametric IR-generation [125,3,148,149,7,103,206], far-IR-free electron lasers [162,86,163,195] and inter-band optical excitation [94]. In these experiments the "pump" pulse creates a population of excited carriers, whilst a much weaker "probe" pulse measures the absorption (transmission).…”

“…3 shows photoluminescence and spectral response measurements for an unimplanted-annealed and an implanted-annealed QWIP. The photolumi nescence full-width-half-maximum (FWHM) of the annealed sample (b) reduces significantly compared with the reference sample (a).…”

Direct observation of intersubband relaxation dynamics and application to subpicosecond all-optical modulation

“…We have experimentally demonstrated the modulation scheme in GaAdAlGaAs QWs, and observed an ultrafast response time of -Ips (FWHM), which agrees with the the01-y. '~' However, the modulation characteristics also contain a slowly tailing component with a relaxation time of [3][4][5] ps, which is undesirable for the applications such as ultra high-bit-rate de-multiplexers used in optical communication systems.…”