Search

We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz-Keldysh geometry at wavelengths of 0.92-0.94 μm. A maximum two-wave mixing gain of 138 cm[sup -1] and a maximum diffraction efficiency of 1.5x10[sup -4] are obtained. The saturation intensity and the spatial resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law. © 2001 American Institute of Physics. We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz-Keldysh geometry at wavelengths of 0.92-0.94 μm. A maximum two-wave mixing gain of 138 cm[sup -1] and a maximum diffraction efficiency of 1.5x10[sup -4] are obtained. The saturation intensity and the spatial ! resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law. © 2001 American Institute of Physics. We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz-Keldysh geometry at wavelengths of 0.92-0.94 μm. A maximum two-wave mixing gain of 138 cm[sup -1] and a maximum diffraction efficiency of 1.5x10[sup -4] are obtained. The saturation intensity and the spatial resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated intersubband absorption of GaN/Al0.58Ga0.42N multiple quantum well structures of high quality, which were grown by low-pressure metal organic chemical vapor deposition (MOCVD). The crystalline quality and uniformity of the AlGaN barriers were improved by suppressing gas-phase parasitic reaction between NH3 and TMAl. This, in turn, produced a very sharp intersubband absorption spectrum with a spectral linewidth as narrow as 35 meV. [Copyright &y& Elsevier]

Magnetotransport properties of modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures were investigated by means of magnetoresistance measurements at low temperatures and high magnetic fields. Strong Shubnikov-de Haas oscillations with the double periodicity are observed. The mobility spectrum is obtained, which demonstrates that the mobilities of the two-dimensional electron gas (2DEG) in the two subbands in the triangular quantum well at heterointerface. It is found that the mobility of the 2DEG in the second subband is much higher than that in the first one. This is explained that interface roughness scattering and alloy disorder scattering have much stronger influence on transport properties of the 2DEG in the first subband than that in the second subband in Al[sub x]Ga[sub 1-x]N/GaN heterostructures. [ABSTRACT FROM AUTHOR]

A way of analyzing the data in a variable stripe length method gain experiment is presented. We confirm that the stripe length dependence of the gain in In[sub 0.02]Ga[sub 0.98]N/In[sub 0.16]Ga[sub 0.84]N multiple quantum wells is caused by the change of the chemical potential along the excited stripe due to the interaction of the carrier and photon densities, and the gain threshold density is estimated. A trial function assuming a Lorentzian line shape for the stripe length dependence of the gain is compared with the edge emission intensity as a function of the stripe length. This is found to fit very well with our data, even beyond the saturation region. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectra were measured for sub-nanometer-thick GaN quantum wells (QWs) with Al[sub 0.8]Ga[sub 0.2]N barriers, which were grown by atmospheric-pressure metal-organic chemical-vapor deposition. The thickness of the GaN QW layers was systematically varied from 1 to 4 ML. We clearly observed a PL peak at room temperature at a wavelength as short as 247 nm (5.03 eV) from 1-ML-thick QWs. The effective confinement energy, or difference between this recombination energy and the band gap of bulk GaN, is as large as 1.63 eV. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report photoluminescence (PL) and time-resolved PL measurements of GaN/Al[sub x]Ga[sub 1-x]N multiple quantum wells with barriers of high aluminum content, x=0.5. In wells of width 1-2 nm, low temperature recombination appears to be dominated by radiative processes with lifetimes ∼0.5 ns. Dependence of lifetime on emission energy is very small compared to InGaN quantum wells, indicating that carrier localization is very slight and interface quality is high. In 4 nm wells, PL emission at an energy below the bulk GaN band gap and long recombination lifetimes result from the polarization field across the wells. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Kerr gate technique is used to time-resolve the gain in an In0.02Ga0.98N/In0.16Ga0.84N multiple quantum well sample. A new way of analyzing the data in such a variable stripe length method gain experiment is used to analyze both the time-integrated and time-resolved spectra. We confirm that the stripe length dependence of the gain in the multiple quantum wells under nanosecond excitation is caused by the change of the chemical potential along the excited stripe due to the interaction of the carrier and photon densities, and the gain threshold density is estimated. A trial function assuming a Lorentzian line shape for the stripe length dependence of the gain is compared with the edge emission intensity. This is found to fit very well with our data, even beyond the saturation region. Furthermore, we have extended the investigation to examine the dynamics of the emission and gain. These measurements suggest that the photoexcited carriers must localize (possibly at indium-rich sites) before strong stimulated emission is seen. [Copyright &y& Elsevier]

Transport properties of the two-dimensional electron gas (2DEG) in AlxGa1−xN/GaN heterostructures were investigated by means of magnetotransport measurements. The mobilities corresponding to the 2DEG in the first and the second subbands in the trianglar quantum well at the heterointerface were obtained. When the AlxGa1−xN barrier is partially relaxed, the mobility of the 2DEG in the first subband decreases significantly, but there is an increase of mobility in the second subband. We suggest that the scattering from the piezoelectric polarization field modulated by the misfit dislocations at the heterointerface is responsible for the decrease of the 2DEG mobility. Meanwhile, the 2DEG in the second subband leaves farther from the heterointerface than that in the first subband, and thus suffers weaker scattering from the heterointerface roughness and the modulated polarization field. Therefore, the mobility of the 2DEG in the second subband is much higher than that in the first subband. [Copyright &y& Elsevier]

The Kerr gate technique is used to time-resolve the gain in an In0.02Ga0.98N/In0.16Ga0.84N multiple quantum well sample. A new way of analyzing the data in such a variable stripe length method gain experiment is used to analyze the time-resolved spectra. The dynamics of the emission and gain are discussed. These measurements suggest that the photoexcited carriers must localize (possibly at indium-rich sites) before strong stimulated emission is seen. [Copyright &y& Elsevier]