Tunnel-regenerated multiple-active-region light-emitting diodes with high efficiency

Tunnel-regenerated multiple-active-region (TRMAR) light-emitting diodes (LEDs) with high quantum efficiency and high brightness have been proposed and fabricated. We have proved experimentally that the efficiency of the electrical luminescence and the on-axis luminous intensity of such TRMAR LEDs scaled linearly approximately with the number of the active regions. The on-axis luminous intensity of such TRMAR LEDs with only 3 mum GaP current spreading layer have exceeded 5 cd at 20 mA dc operation under 15 degrees package. The high-quantum-efficiency and high-brightness LEDs under the low injection level were realized. (C) 2001 American Institute of Physics.

Impurity-free vacancy diffusion technique for InGaAsP/InP multiple quantum well laser structure

Bandgap tuning of the InGaAsP/InP multiple quant um well (MQW) laser structure by the impurity-free vacancy diffusion (IFVD) is investigated using photoluminescence. It has been demonstrated that the effects of the plasma bombardment to the:sample surface involved in the IFVD technique can enhance the intermixing of the InGaAsP/InP MQW laser structure. The reliability of the IFVD technique, particularly the effects of the surface decomposition and the intrinsic defects formed in the growth or preparation of the wafer, has been discussed.

Back-incident SiGe-Si multiple quantum-well resonant-cavity-enhanced photodetectors for 1.3-mu m operation

A back-incident Si-0.65 Ge-0.35/Si multiple quantum-well resonant-cavity-enhanced photodetector operating near 1.3 mum is demonstrated on a separation-by-implantation-oxygen substrate. The resonant cavity is composed of an electron-beam evaporated SiO2-Si distributed Bragg reflector as a top mirror and the interface between the buried SiO2 and the Si substrate as a bottom mirror. We have obtained the responsivity as high as 31 mA/WI at 1.305 mum and the full width at half maximum of 14 nm.

Evolution from point defects to arsenic clusters in low-temperature grown GaAs/AlGaAs multiple quantum wells

Optical transient current spectroscopy (OTCS), photoluminescence (PL) spectroscopy and excitonic electroabsorption spectroscopy have been used to investigate the evolution of defects in the low-temperature grown GaAs/AlGaAs multiple quantum well structures during the postgrowth rapid thermal annealing. The sample was grown at 350 degrees C by molecular beam epitaxy on miscut (3.4 degrees off (001) towards (111)A) (001) GaAs substrate. After growth, the sample was subjected to 30s rapid thermal annealing in the range of 500-800 degrees C. It is found that the integrated PL intensity first decreases with the annealing temperature, then gets a minimum at 600 degrees C and finally recovers at higher temperatures. OTCS measurement shows that besides As,, antisites and arsenic clusters, there are several relatively shallower deep levels with excitation energies less than 0.3 eV in the as-grown and 500 degrees C-annealed samples. Above 600 degrees C, OTCS signals from As,, antisites and shallower deep levels become weaker, indicating the decrease of these defects. It is argued that the excess arsenic atoms group together to form arsenic clusters during annealing. (C) 2000 Elsevier Science B.V. All rights reserved.

Characteristics of circular waveguide photodetectors using SiGe/Si multiple quantum wells

We report on the fabrication of circular waveguide photodetectors with a response near 1.3 mu m wavelength using SiGe/Si multiple quantum wells. The quantum efficiency of the circular waveguide photodetector is improved when compared with that of the rib waveguide photodetector in the same wavelength at 1.3 mu m The frequency response of the photodetectors is simulated. The emciency-bandwidth product of the circular waveguide photodetectors is improved correspondingly. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Photoelectrochemical behavior of a novel composite In0.15Ga0.85As/GaAs vertical bar GaAs/Al0.3Ga0.7As multiple quantum well electrode

A novel composite InxGa1-xAs/GaAs/GaAs/AlxGa1-xAs multiple quantum well material with different well widths was studied as a new kind of photoelectrode in a photoelectrochemical cell. The photocurrent spectrum and photocurrent-electrode potential curve were measured in ferrocene nonaqueous solution. Pronounced quantization effects and strong exciton absorption were observed in the photocurrent spectrum. The effects of surface states and interfacial states on the photocurrent-electrode potential curve are discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

Observation of quantum-confined Stark shifts in SiGe/Si type-I multiple quantum wells

Quantum-confined Stark shifts in SiGe/Si type-I multiple quantum wells are suggested by the bias dependence of the photocurrent spectra of p-i-n photodiodes. Both Stark redshift and blueshift have been observed for the same sample in the different ranges of electric fields applied to the quantum wells. The turnaround point corresponds to a certain electric field (named "critical" field). This phenomenon was generally predicted by Austin in 1985 [Phys. Rev. B 31, 5569 (1985)] and calculated in detail for SiGe quantum structure by Kim recently [Thin Solid Films 321, 215 (1998)]. The critical electric field obtained from the photocurrent spectra is in reasonable agreement with the theoretical prediction. (C) 2000 American Institute of Physics. [S0021-8979(00)03711-7].

Infrared absorption efficiency in AlAs/AlxGa1-xAs type-II multiple-quantum-well structure grown on (211) GaAs substrate

We have made a normal incidence high infrared absorption efficiency AlAs/Al0.55Ga0.45As multiple-quantum-well structure grown on (211) GaAs substrates by molecular beam epitaxy (MBE). A strong infrared absorption signal at 11.6 mu m due to the transition of the ground state to the first excited state, and a small signal at 6.8 mu m due to the transition from the ground state to continuum. were observed. A 45 degrees tilted incidence measurement was also performed on the same sample for the comparison with a normal incidence measurement. Both measurements provide important information about the quantum well absorption efficiency. Efficiencies which evaluate the absorption of electric components perpendicular and parallel to the well plane are eta(perpendicular to) = 25% and eta(parallel to) = 88%, respectively. The total efficiency is then deduced to be eta = 91%. It is apparent that the efficiency eta(parallel to) dominates the total quantum efficiency eta Because an electron in the (211) AlAs well has a small effective mass (m(zx)* or m(zy)*), the normal incidence absorption coefficient is expected to be higher:than that grown on (511) and (311) substrates. Thus, in the present study, we use the (211) substrate to fabricate QWIP. The experimental results indicate the potential of these novel structures for use as normal incidence infrared photodetectors.

Observation of field-driven blue shift in delta-doped Si n-i-p-i multiple quantum wells

We report the observation of the field-driven blue shift at near absorption edge in the photo-current response spectra of delta-doped Si n-i-p-i multiple quantum wells due to the widening of the effective energy gap. This phenomenon differs from the observed results in GaAs/AlGaAs and GeSi/Si superlattices, because the physical mechanisms of forming energy band in these superlattice samples are different. Our experimental results are interpreted satisfactorily by the theoretical calculation. (C) 1999 Elsevier Science Ltd. All rights reserved.

Influence of (001) vicinal GaAs substrates on the optical properties of defects in low-temperature grown GaAs/AlGaAs multiple quantum wells

Photoluminescence (PL) spectroscopy and carrier lifetime measurement has been used to characterize optical properties of defects in the low-temperature (LT) grown GaAs/AlGaAs multiple quantum well structures. Two sets of samples were grown at 400 degrees C by molecular beam epitaxy on nominal (001) and miscut [4 degrees off (001) towards (111) A] GaAs substrates, respectively. After growth, samples were subjected to 30 s rapid thermal annealing at 600-800 degrees C. It is found that after annealing, two defect-related PL features appear in the samples grown on nominal (001) GaAs substrates, but not in those grown on miscut (001) GaAs substrates. The carrier lifetimes are about 31 and 5 ps in as-grown samples grown on nominal and miscut (001) GaAs substrates, respectively. The different PL spectra and carrier lifetimes in two sets of samples are attributed to different structures of the As-Ga-like defects formed during LT growth. (C) 1999 American Institute of Physics. [S0003-6951(99)00230-2].

High-field cyclotron resonance and electron-phonon interaction in modulation-doped multiple quantum well structures

A systematic study of electron cyclotron resonance (CR) in two sets of GaAs/Al0.3Ga0.7As modulation-doped quantum-well samples (well widths between 12 and 24 nm) has been carried out in magnetic fields up to 30 T. Polaron CR is the dominant transition in the region of GaAs optical phonons for the set of lightly doped samples, and the results are in good agreement with calculations that include the interaction with interface optical phonons. The results from the heavily doped set are markedly different. At low magnetic fields (below the GaAs reststrahlen region), all three samples exhibit almost identical CR which shows little effect of the polaron interaction due to screening and Pauli-principle effects. Above the GaAs LO-phonon region (B > similar to 23 T), the three samples behave very differently. For the most lightly doped sample (3 x 10(11) cm(-2)) only one transition minimum is observed, which can be explained as screened polaron CR. A sample of intermediate density (6 x 10(11) cm(-2)) shows two lines above 23 T; the higher frequency branch is indistinguishable from the positions of the single line of the low density sample. For the most heavily, doped sample (1.2 x 10(12) cm(-2)) there is no evidence of high frequency resonance, and the strong, single line observed is indistinguishable from the lower branch observed from sample with intermediate doping density. We suggest that the low frequency branch in our experiment is a magnetoplasmon resonance red-shifted by disorder, and the upper branch is single-particle-like screened polaron CR. (C) 1998 Elsevier Science B.V. All rights reserved.

Buried heterostructure InGaAsP/InP strain-compensated multiple quantum well laser with a native-oxidized InAlAs current blocking layer

An InAlAs native oxide is used to replace the p-n reverse-biased junction in a conventional buried heterostructure InP-based laser. This technique reduces the number of regrowth steps and eliminates leakage current under high-temperature operation. The InAlAs native oxide buried heterostructure (NOBH) laser with strain-compensated InGaAsP/InP multiple quantum well active layers has a threshold current of 5.6 mA, a slope efficiency of 0.23 mW/mA, and a linear power up to 22.5 mW with a HR-coated facet. It exhibits single transverse mode with lasing wavelength at 1.532 mu m. A characteristic temperature (T-0) of 50 K is obtained from the NOBH laser with a nonoptimized oxide layer width. (C) 1998 American Institute of Physics. [S0003-6951(98)01352-7].

Linewidth of the infrared absorption spectra due to bound-to-continuum transition in GaAs/AlxGa1-xAs multiple quantum well structures

We have observed an extremely narrow absorption spectrum due to bound-to-continuum transition in GaAs/AlxGa1-xAs multiple quantum wells (MQWs). Its linewidth is only about one tenth of the values reported previously. Our calculation indicates that the broadening of the excited state in the continuum has little contribution to the absorption linewidth. We have grown a sample whose MQW region contains two kinds of wells with a minor thickness inhomogeneity. Its resultant absorption linewidth is six times as large as that of homogeneous well sample, which is in good agreement with our theoretical analysis. Thus we can suggest that the wider absorption spectra reported by many authors may be due to the well width inhomogeneity. (C) 1998 American Institute of Physics. [S0003-6951(98)03430-5]

Resonant magnetopolaron effects in GaAs/AlGaAs multiple quantum well structures

A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons. (C) 1998 Elsevier Science B.V. All rights reserved.

Photoluminescence investigation of GaInP/GaAs multiple quantum wells grown on (001) and (311) B GaAs surfaces by gas source molecular beam epitaxy

Photoluminescence (PL) investigation was carried out on GaInP/GaAs multiple quantum wells structures grown on (001) and (311) B surfaces of GaAs by gas source molecular beam epitaxy. Superlattice structures of GaAs/GaInP grown on (001) GaAs substrate were also studied in comparison. Deep-level luminescence was seen to dominate the PL spectra from the quantum wells and superlattice structures that were grown on (001) GaAs substrate. In contrast, superior optical properties were exhibited in the same structures grown on (311) B GaAs surfaces. The results suggested that GaAs/GaInP quantum well structures on (311) B oriented substrates could efficiently suppress the deep-level emissions, result in narrower PL peaks indicating smooth interfaces. (C) 1998 American Institute of Physics.