Intersubband relaxation dynamics inGaN∕AlNmultiple quantum wells studied by two-color pump-probe experiments

We have investigated intersubband relaxation in $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ multiple quantum wells using a two-color pump-probe technique in a wide energy range around $800\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ $(1.55\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$. We have observed not only absorption bleaching signals but also, for the first time, induced absorption signals with an ultrafast and a slow component. Absorption bleaching signals are attributed to a phase space filling of the upper subband and a carrier cooling process in the lower subband, with relaxation times of $140\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ and $300\char21{}400\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$, respectively. The ultrafast induced absorption corresponds to the absorption of electrons during intra-subband relaxation and the slow component of $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ corresponds to the carrier cooling process. We have also found that the intrinsic absorption width of highly doped materials is as large as the inhomogeneous width, because the dispersion difference of subbands is enhanced by exchange interaction.

[1]  Ryoichi Akimoto,et al.  Short-wavelength (λ<2 μm) intersubband absorption dynamics in ZnSe/BeTe quantum wells , 2002 .

[2]  Woerner,et al.  Nonequilibrium Dynamics in a Quasi-Two-Dimensional Electron Plasma after Ultrafast Intersubband Excitation. , 1996, Physical review letters.

[3]  Jerry R. Meyer,et al.  Band parameters for III–V compound semiconductors and their alloys , 2001 .

[4]  Norio Iizuka,et al.  Feasibility Study on Ultrafast Nonlinear Optical Properties of 1.55-µ m Intersubband Transition in AlGaN/GaN Quantum Wells , 1997 .

[5]  J. Hamazaki,et al.  Ultrafast intersubband relaxation and nonlinear susceptibility at 1.55 μm in GaN/AlN multiple-quantum wells , 2004 .

[6]  Susumu Noda,et al.  Carrier relaxation dynamics in an ultrafast all-optical modulator using an intersubband transition , 2001 .

[7]  Susumu Noda,et al.  Pump-probe measurement of ultrafast all-optical modulation based on intersubband transition in n-doped quantum wells , 2000 .

[8]  Thomas Elsaesser,et al.  Homogeneous broadening and excitation-induced dephasing of intersubband transitions in a quasi-two-dimensional electron gas , 2001 .

[9]  Claire F. Gmachl,et al.  Intersubband absorption at λ∼1.55 μm in well- and modulation-doped GaN/AlGaN multiple quantum wells with superlattice barriers , 2000 .

[10]  J. Shah.  Ultrafast spectroscopy of semiconductors and semiconductor nanostructures , 1996 .

[11]  Katsumi Kishino,et al.  Intersubband transition in (GaN)m/(AlN)n superlattices in the wavelength range from 1.08 to 1.61 μm , 2002 .

[12]  Claire F. Gmachl,et al.  Resonant optical nonlinearities from intersubband transitions in GaN/AlN quantum wells , 2003 .

[13]  Teruo Mozume,et al.  Ultralow Intersubband Absorption Saturation Intensity at Communication Wavelength Achieved in Novel Strain Compensated InGaAs/AlAs/AlAsSb Quantum Wells Grown by Molecular Beam Epitaxy , 2003 .

[14]  O. Byungsung,et al.  Exchange interactions in quantum well subbands , 1988 .

[15]  Joerg Heber,et al.  Comparative study of ultrafast intersubband electron scattering times at ̃1.55 μm wavelength in GaN/AlGaN heterostructures , 2002 .

[16]  Francois H. Julien,et al.  Intersubband spectroscopy of doped and undoped GaN/AlN quantum wells grown by molecular-beam epitaxy , 2003 .

[17]  Kei Kaneko,et al.  Near-infrared intersubband absorption in GaN/AlN quantum wells grown by molecular beam epitaxy , 2002 .

[18]  T. Hasama,et al.  Sub-picosecond electron relaxation of near-infrared intersubband transitions in n-doped (CdS/ZnSe)/BeTe quantum wells , 2002 .

[19]  Norio Iizuka,et al.  Electron Scattering Rates in AlGaN/GaN Quantum Wells for 1.55-µm Inter-Subband Transition , 1998 .

[20]  Katsumi Kishino,et al.  Improved Molecular Beam Epitaxy for Fabricating AlGaN/GaN Heterojunction Devices , 2002 .

[21]  Osamu Wada,et al.  Ultrafast intersubband relaxation (⩽150 fs) in AlGaN/GaN multiple quantum wells , 2000 .

[22]  Woerner,et al.  Nonlinear intersubband absorption of a hot quasi-two-dimensional electron plasma studied by femtosecond infrared spectroscopy. , 1996, Physical review. B, Condensed matter.

[23]  Jackson,et al.  Absorption edge singularities in highly excited semiconductors. , 1992, Physical review letters.