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18 Nov 1991

Volume 59, Issue 21, pp. 2631-2762

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Dynamic optical switching of symmetric self‐electro‐optic effect devices

G. D. Boyd, L. M. F. Chirovsky, and R. A. Morgan

Appl. Phys. Lett. 59, 2631 (1991); http://dx.doi.org/10.1063/1.105920 (3 pages) | Cited 8 times

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We describe a new method of operation of symmetric self‐electro‐optic effect devices (S‐SEEDs) using excitation pulses shorter than the diode sweep out times. We shall call this dynamic SEED switching. Previous SEEDs are optically bistable logic devices which use the unique properties of multiple quantum well structures placed in the intrinsic i regions of two p‐i‐n diodes reverse biased in series. Conventional operation of S‐SEEDs is at the exciton wavelength where absorption decreases with increasing electric field. Utilizing the dynamic properties of the S‐SEED we demonstrate that switching is possible at any wavelength where there is a nonlinear response showing a threshold. The major advantages of dynamic over conventional operation, is that it can be faster while requiring less optical energy, is automatically reset each cycle, and is less susceptible to saturation.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

GaAs‐based diode lasers on Si with increased lifetime obtained by using strained InGaAs active layer

H. K. Choi, C. A. Wang, and N. H. Karam

Appl. Phys. Lett. 59, 2634 (1991); http://dx.doi.org/10.1063/1.105921 (2 pages) | Cited 21 times

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Strained InGaAs/AlGaAs quantum well diode lasers have been fabricated on Si substrates for the first time. A GaAs buffer layer was grown on each Si wafer by temperature‐cycled organometallic vapor phase epitaxy (OMVPE). The wafer was then transferred to a second reactor for OMVPE growth of a graded‐index separate‐confinement heterostructure single‐quantum well laser structure. For lasers with a cavity length of 1000 μm, room‐temperature pulsed threshold current densities as low as 174 and 195 A/cm2 have been obtained for active layer compositions of In0.02Ga0.98As and In0.05Ga0.95As, respectively. One laser with an In0.05Ga0.95As active layer operated cw for 56.5 h, a record lifetime for GaAs‐based diode lasers on Si.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Possibility of infrared laser in a resonant tunneling structure

A. Kastalsky, V. J. Goldman, and J. H. Abeles

Appl. Phys. Lett. 59, 2636 (1991); http://dx.doi.org/10.1063/1.105922 (3 pages) | Cited 40 times

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We analyze the possibility of creating population inversion and optical gain in a specially designed resonant tunneling superstructure when the energy between active quantum levels is greater than the optical phonon energy. Each of twenty periods of the structure represents a complete resonant tunneling, double quantum well diode designed to provide escape time from the lower level of the active well much shorter than the electron‐optical phonon relaxation time. Three heterostructure materials are considered: InAs/AlSb, InGaAs/AlAs, and GaAs/AlAs. In all three cases optical gains of 50–90 cm−1 were calculated to be present for the photon energy of ≊0.1 eV.
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42.55.Px Semiconductor lasers; laser diodes
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Coherent infrared fiber image bundle

Junji Nishii, Toshiharu Yamashita, Takashi Yamagishi, Chinari Tanaka, and Hiroshi Sone

Appl. Phys. Lett. 59, 2639 (1991); http://dx.doi.org/10.1063/1.105923 (3 pages) | Cited 16 times

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Coherent infrared (IR) image bundle was developed for the delivery of the IR thermal image. The fiber employed was the As2S3 glass core of 65 μm diam and Teflon (perfluoronated ethylene propylene) cladding of 75 μm diam, which has the transmission range in the wavelength region between 1 and 7 μm. Two kinds of bundles of 100 cm long were prepared, which consisted of 1550 fibers (NPB75‐1550) and of 8400 fibers (NPB75‐8400). The IR imaging system was constructed by coupling the bundle to an IR television camera. The performance of the system was investigated by detecting the thermal image of an operating LSI package.
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42.30.-d Imaging and optical processing
42.81.-i Fiber optics
87.63.Hg Thermography

High‐power operation of strained InGaAs/AlGaAs single quantum well lasers

A. Moser, A. Oosenbrug, E. E. Latta, Th. Forster, and M. Gasser

Appl. Phys. Lett. 59, 2642 (1991); http://dx.doi.org/10.1063/1.105924 (3 pages) | Cited 28 times

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The high‐power integrity of strained single quantum well InGaAs/AlGaAs lasers grown by molecular beam epitaxy is investigated. In the high‐power regime, the lifetime of the Lz=7 nm strained quantum well laser emitting at ≂ 980 nm is found to be limited by the air‐cleaved facets. However, a comparison with lattice‐matched 7 nm quantum well GaAs/AlGaAs lasers, which otherwise have an almost identical vertical structure shows a substantial lifetime improvement. This indicates that lattice hardening due to the indium in the quantum well is effective in the facet region. The investigations demonstrate the feasibility of 150 mW single mode operation with sufficient lifetime for practical applications in the wavelength range of ≂1 μm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
61.72.U- Doping and impurity implantation
68.35.Md Surface thermodynamics, surface energies

Novel all‐optical 10 μm waveguide modulator based on intersubband absorption in GaAs/AlGaAs quantum wells

F. H. Julien, P. Vagos, J.‐M. Lourtioz, D. D. Yang, and R. Planel

Appl. Phys. Lett. 59, 2645 (1991); http://dx.doi.org/10.1063/1.105925 (3 pages) | Cited 15 times

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Efficient all‐optical modulation of mid‐infrared radiations based on photoinduced intersubband absorption of a GaAs/AlGaAs multiquantum well structure is demonstrated at room temperature. The sample designed for mid‐infrared waveguiding was grown by molecular beam epitaxy. A double‐resonance spectroscopy of both interband and intersubband transitions of the quantum wells is presented. The intersubband resonance is found at 9.56 μm. An AlGaAs laser diode is used to optically pump the quantum wells. On/off modulation ratios as high as 150:1 are obtained with only 45 mW pump power and for mid‐infrared input powers up to 0.5 W. The frequency bandwidth of the device is presently comparable to that of acousto‐optic modulators available at mid‐infrared wavelengths.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers

Surface‐emitting laser‐based optical bistable switching device

Ping Zhou, Julian Cheng, S. Z. Sun, C. F. Schaus, C. Hains, D. R. Myers, and G. A. Vawter

Appl. Phys. Lett. 59, 2648 (1991); http://dx.doi.org/10.1063/1.105926 (3 pages) | Cited 1 time

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The first experimental demonstration of a surface‐normal bistable optical switching device based on the monolithic integration of a vertical‐cavity surface‐emitting laser and a pnpn photothyristor is reported. By the use of ion implantation, it is shown that the positive feedback in the photothyristor can be controlled, thus enabling the integration of both bistable and latching optical switches on the same epitaxial structure. High contrast (30 dB) and an optical gain of 8 are demonstrated.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
85.60.-q Optoelectronic devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Femtosecond response of electro‐optic poled polymers

Paul M. Ferm, Charles W. Knapp, Chengjiu Wu, James T. Yardley, Bin‐Bin Hu, Xi‐Cheng Zhang, and David H. Auston

Appl. Phys. Lett. 59, 2651 (1991); http://dx.doi.org/10.1063/1.105927 (3 pages) | Cited 8 times

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We investigate the ultrafast electro‐optic response and sensitivity of a poled side chain polymer film via the electro‐optic sampling technique. A 760 fs rise‐time electrical transient is observed corresponding to a bandwidth of 460 GHz. We believe this to be device limited and not due to limitations in the speed of response of the polymer.
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78.20.Jq Electro-optical effects
42.70.-a Optical materials

Polarization‐dependent optical nonlinearities in fractional‐layer superlattices

A. Chavez‐Pirson, J. Yumoto, H. Ando, T. Fukui, and H. Kanbe

Appl. Phys. Lett. 59, 2654 (1991); http://dx.doi.org/10.1063/1.105928 (3 pages) | Cited 5 times

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We measure the room‐temperature polarization‐dependent nonlinear absorption and refractive‐index spectra of a (Al0.5Ga0.5As)1/2(GaAs)1/2 fractional‐layer superlattice (FLS) structure grown by metalorganic chemical vapor deposition. The anisotropic nonlinear effects between the directions parallel and perpendicular to the superlattice give rise to a nonlinear optical birefringence in the plane of the growth surface. From our measurements using a femtosecond optical pulse, we derive the magnitude and spectral shape of the nonlinear optical birefringence. We describe the basis of an all‐optical polarization rotation switch using the FLS structure.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Periodically poled LiNbO3 for high‐efficiency second‐harmonic generation

D. H. Jundt, G. A. Magel, M. M. Fejer, and R. L. Byer

Appl. Phys. Lett. 59, 2657 (1991); http://dx.doi.org/10.1063/1.105929 (3 pages) | Cited 41 times

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Quasi‐phase‐matched room‐temperature frequency doubling to generate blue, green, and red light was demonstrated using periodically poled LiNbO3 crystals. A 1.24‐mm‐long sample in an external resonant cavity generated 1.7 W of green power from an input of 4.2 W at the 1.064 μm Nd:YAG laser line when heated to 140 °C to compensate for a slight error in periodicity.  
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.-a Optical materials
81.40.Tv Optical and dielectric properties related to treatment conditions

Threshold and saturation effects for photosignals in an amorphous silicon waveguide structure

M. Zelikson, K. Weiser, J. Salzman, and J. Kanicki

Appl. Phys. Lett. 59, 2660 (1991); http://dx.doi.org/10.1063/1.105931 (3 pages) | Cited 2 times

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We report on a novel photosignal effect when laser light enters an amorphous hydrogenated silicon (a‐Si:H) core waveguide and an external voltage is applied. Above a threshold voltage, the electric field separates the photocarriers in the a‐Si:H layer so that the voltage across it is reduced. For larger voltages or high light intensities, this screening effect saturates. Analysis of the results yields electron and hole drift mobilities of 0.6 and 0.2 cm2/V s), respectively.
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42.79.Gn Optical waveguides and couplers
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Pz Photoconduction and photovoltaic effects

Monolithic two‐dimensional surface‐emitting diode laser arrays mounted in the junction‐down configuration

M. Jansen, J. J. Yang, S. S. Ou, M. Sergant, L. Mawst, J. Rozenbergs, J. Wilcox, and D. Botez

Appl. Phys. Lett. 59, 2663 (1991); http://dx.doi.org/10.1063/1.105932 (3 pages)

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We report on the first achievement of large area (0.5 cm2) monolithic two‐dimensional surface‐emitting arrays mounted in the junction‐down configuration. Device fabrication involves dry etching of 45°, and vertical micromirrors with ±2° tolerances and <0.2 μm RMS smoothness, integration of 100‐μm‐thick current‐spreading electrodes for minimizing ohmic loss, large area packaging, and mounting to heat exchangers for long pulse and minimum chirp operation. Uniform lasing is achieved from 0.2×0.5 cm2 and 0.5×1 cm2 active area junction‐down monolithic arrays (120 and 600 emitters, respectively) using 100 μs long pulses at a 1% duty cycle. Differential quantum efficiencies of ≥ (R18)40% and 7% are achieved for rows of 12 emitters, and for 0.2×0.5 cm2 active area arrays, respectively. The decrease in efficiency with increased area is found to be due to current leakage, which in turn limits the 2‐D array emitted optical‐power density to 150 W/cm2. Wavelength chirp in these devices is measured to be <4 nm at twice the threshold current.
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42.82.-m Integrated optics
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Measurements of nondegenerate optical nonlinearity using a two‐color single beam method

H. Ma, A. S. L. Gomes, and Cid B. de Araujo

Appl. Phys. Lett. 59, 2666 (1991); http://dx.doi.org/10.1063/1.105933 (3 pages) | Cited 59 times

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A two‐color ‘‘z’’ scan method is introduced to characterize the nonlinear refraction of optical materials in their absorptive region. We demonstrate the method by measuring the sign and the magnitude of the frequency nondegenerate nonlinearity in the absorptive region of semiconductor doped glasses.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Optical gain of CdZnSe/ZnSe quantum well lasers

D. Ahn, T.‐K. Yoo, and H. Y. Lee

Appl. Phys. Lett. 59, 2669 (1991); http://dx.doi.org/10.1063/1.105901 (3 pages) | Cited 10 times

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Polarization‐dependent optical gain of recently demonstrated CdZnSe/ZnSe quantum well lasers is calculated for the first time. Our analysis is based on the multiband effective mass theory (k⋅p theory) and the density matrix formalism with intraband relaxation taken into account. It is shown theoretically that the TE mode gain is significantly larger than the TM mode gain for a wide range of carrier density. Comparison of the room‐temperature TE mode gain of CdZnSe/ZnSe quantum well with that of GaAs/AlGaAs quantum well gives disappointing results for the II‐VI semiconductor lasers. It is expected that the optical gain of the ZnSe‐based semiconductor lasers would be substantially smaller than the optical gain of the GaAs‐based semiconductor lasers for a same quantum well width and carrier density.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
71.55.Gs II-VI semiconductors

Soft x‐ray spectra produced by subpicosecond laser‐double‐pulses

U. Teubner, G. Kühnle, and F. P. Schäfer

Appl. Phys. Lett. 59, 2672 (1991); http://dx.doi.org/10.1063/1.105902 (3 pages) | Cited 34 times

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See Also: Erratum

Show Abstract
Soft x‐ray spectra generated on flat Al targets by a 500 fs KrF∗ laser pulse (intensity 5.3×1015 W/cm2), preceded by a prepulse of the same pulse duration, have been measured as a function of the pulse separation and the prepulse intensity. It was found that not only the total x‐ray emission was much stronger when the prepulse was present but, in particular, lines in the shorter wavelength region had a higher intensity than without prepulse, and were strongly dependent on the time separation between the prepulse and the main pulse.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.-r Laser-plasma interactions
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
42.55.Vc X- and γ-ray lasers

Control of hydrocarbon radicals and film deposition by using a whistler wave discharge in range of radio frequency

T. Mieno, T. Shoji, and K. Kadota

Appl. Phys. Lett. 59, 2675 (1991); http://dx.doi.org/10.1063/1.105903 (3 pages) | Cited 6 times

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Production of hydrocarbon radicals is controlled by using a whistler wave discharge in range of radio frequency in a low pressure region (∼0.1 Pa). Plasma density of 1010–1013 cm−3, electron temperature of 2–20 eV is obtained for the discharge of the admixture of Ar and small content of source gases (CH4, C2H2, CO). Spectroscopic measurement indicates that densities of CH and H radicals and the deposition rate of amorphous carbon:H film increase with electron density, electron temperature, and source gas pressure. The etching effect of H atoms influences on the deposition rate and a high deposition rate (90 μm/h for CO/Ar discharge) is obtained even in a low neutral pressure discharge.
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52.80.-s Electric discharges
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Ellipsometric determination of the optical constants of C60 (Buckminsterfullerene) films

S. L. Ren, Y. Wang, A. M. Rao, E. McRae, J. M. Holden, T. Hager, KaiAn Wang, Wen‐Tse Lee, H. F. Ni, J. Selegue, and P. C. Eklund

Appl. Phys. Lett. 59, 2678 (1991); http://dx.doi.org/10.1063/1.105907 (3 pages) | Cited 135 times

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We report the first ellipsometric measurement of the fundamental optical constants (n,k) of C60 films deposited on Si(100) and Au overcoated Si(100) substrates. We obtain a highest occupied molecular orbital‐lowest unoccupied molecular orbit (HOMO‐LUMO) gap value of 2.3 eV, slightly larger than the gap values obtained from the x‐ray photoelectron spectroscopy and electron‐energy‐loss spectroscopy experiments. The structure observed in the UV is discussed in terms of single‐electron excitations across the HOMO‐LUMO gap.
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78.66.-w Optical properties of specific thin films

Generating near‐earth‐core pressures with type‐IIa diamonds

Arthur L. Ruoff, Huan Luo, Craig Vanderborgh, and Yogesh K. Vohra

Appl. Phys. Lett. 59, 2681 (1991); http://dx.doi.org/10.1063/1.105882 (2 pages) | Cited 1 time

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In the past year static pressures of 378 and 416 GPa, greater than the pressure at the center of the earth (361 GPa), were achieved and carefully measured for the first time (x‐ray diffraction on W and Mo, respectively) using extremely high‐quality type‐Ia diamonds (containing nitrogen platelets). In this letter, we show that type‐IIa diamonds (containing no nitrogen) can reach similar pressures (338 GPa by x‐ray diffraction on Pt) thus showing that the strength depends primarily on crystalline perfection (and not on nitrogen platelets). Nearly perfect type‐IIa diamonds are rare.
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62.50.-p High-pressure effects in solids and liquids

Thermal noise current inside a gas of noninteracting charged bosons

H. V. Hickman, A. J. Dekker, and T. M. Chen

Appl. Phys. Lett. 59, 2683 (1991); http://dx.doi.org/10.1063/1.105883 (2 pages)

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An application of Bose–Einstein statistics leads to an expression for the mean‐square value of the spontaneous fluctuations in current that give rise to thermal noise inside a gas of noninteracting charged bosons. Above the Einstein condensation temperature the boson gas thermal noise current is seen to be identical to the corresponding Fermi–Dirac thermal noise current. Below the Einstein condensation temperature, the magnitude of the boson gas thermal noise current decreases as the number of bosons in excited states decreases.
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05.30.Jp Boson systems
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
73.50.Td Noise processes and phenomena
74.90.+n Other topics in superconductivity (restricted to new topics in section 74)

Stress‐driven void growth in narrow interconnection lines

S. M. Hu

Appl. Phys. Lett. 59, 2685 (1991); http://dx.doi.org/10.1063/1.105884 (3 pages) | Cited 5 times

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We consider a model of stress‐driven void growth in interconnection lines that are narrower than the metal grain size. The metal line is imbedded in an SiO2 matrix at a temperature T0, and incurs tensile stress after being brought down to an annealing temperature Tann. A void nucleates at a particular grain boundary, along which the diffusion is assumed to be so fast that the stress relaxation at that grain boundary is nearly complete in a very short time. This is assumed to occur before the void spans the width of the line. Thereafter, the void continues to grow by matter transport through bulk diffusion, cascading down sequential tiers of grain boundaries, resulting in a layer of extra matter at each grain boundary for strain relaxation. The kinetics of the void growth is given analytically. The consideration of climbing dislocations is deferred for future analysis.
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61.72.Bb Theories and models of crystal defects
61.72.Mm Grain and twin boundaries
66.30.Lw Diffusion of other defects
85.40.Ls Metallization, contacts, interconnects; device isolation

Long‐wavelength (1.3 μm) luminescence in InGaAs strained quantum‐well structures grown on GaAs

E. J. Roan and K. Y. Cheng

Appl. Phys. Lett. 59, 2688 (1991); http://dx.doi.org/10.1063/1.105885 (3 pages) | Cited 17 times

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Long‐wavelength (≳1.1 μm) optical emission has been achieved in pseudomorphic InGaAs‐on‐GaAs quantum‐well structure by replacing InGaAs random alloy quantum well with (InAs)n/(GaAs)n short period superlattice (SPS). With the same quantum‐well width, the photoluminescence peak energy of the SPS structure is always smaller than that of the In0.5Ga0.5As random‐alloy structure. Strong photoluminescence was observed in (InAs)1/(GaAs)1 SPS quantum wells with thickness up to 84 Å. The longest optical‐emission wavelength observed in (InAs)1/(GaAs)1 SPS quantum‐well structures at room temperature was 1.34 μm.
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78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Varistor property of n‐BaTiO3 based current limiters

T. R. N. Kutty and V. Ravi

Appl. Phys. Lett. 59, 2691 (1991); http://dx.doi.org/10.1063/1.105886 (3 pages) | Cited 11 times

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Highly stable varistor (voltage‐limiting) property is observed for ceramics based on donor doped ☒Ba1−xSrx☒Ti1−yZryO3 (x<0.35, y<0.05), when the ambient temperature (Ta) is above the Curie point (Tc). If Ta<Tc, the same ceramics showed stable current‐limiting behavior. The leakage current and the breakdown voltage as well as the nonlinearity coefficient (α=30–50) could be varied with the Tc‐shifting components, the grain boundary layer modifiers and the post‐sintering annealing. Analyses of the current‐voltage relations show that grain boundary layer conduction at Ta<Tc corresponds to tunneling across asymmetric barriers formed under steady‐state joule heating. At Ta≳Tc, trap‐related conduction gives way to tunneling across symmetric barriers as the field strength increases.
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72.80.-r Conductivity of specific materials
72.20.Ht High-field and nonlinear effects
73.20.-r Electron states at surfaces and interfaces
73.30.+y Surface double layers, Schottky barriers, and work functions

Depressed index cladding graded barrier separate confinement single quantum well heterostructure laser

T. M. Cockerill, J. Honig, T. A. DeTemple, and J. J. Coleman

Appl. Phys. Lett. 59, 2694 (1991); http://dx.doi.org/10.1063/1.105887 (3 pages) | Cited 11 times

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In this letter, we present data for a novel depressed index cladding laser structure which provides reduced perpendicular far‐field divergence angle with acceptable low‐threshold current densities. Narrow perpendicular divergence angles of 27° full width at half maximum for a nearly perfect Gaussian beam shape have been measured, with a corresponding near‐field spot size of 1.30 μm. Threshold current densities of 309 A/cm2 are observed for 150 μm stripewidth, 780 μm long devices with 0.80 μm transverse spot sizes. Pulsed output powers for unmounted devices are greater than 0.9 W/uncoated facet.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Mv Dye lasers

InGaAs/InP double‐heterojunction bipolar transistors with step graded InGaAsP between InGaAs base and InP collector grown by metalorganic chemical vapor deposition

Michio Ohkubo, Akira Iketani, Tetsurou Ijichi, and Toshio Kikuta

Appl. Phys. Lett. 59, 2697 (1991); http://dx.doi.org/10.1063/1.105888 (3 pages) | Cited 12 times

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We have fabricated InGaAs/InP double‐heterojunction bipolar transistors (DHBTs) grown by metalorganic chemical vapor deposition (MOCVD). By inserting step graded InGaAsP layers between p+‐InGaAs base and n−‐InP collector, the current gain of DHBTs with the graded layers was about twice as large as that without the graded layers, and the dependence of collector current on collector/emitter voltage was smaller than that without graded layers. The current gain was measured up to 2300 with 25×25 μm2 emitter area at a collector current density of 1×104 A/cm2.
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85.30.Pq Bipolar transistors
68.55.-a Thin film structure and morphology

Cathodoluminescence observation of excitons confined to a two‐dimensional electron gas in a selectively doped heterostructure

C. L. Reynolds, S. E. Lengle, and V. Swaminathan

Appl. Phys. Lett. 59, 2700 (1991); http://dx.doi.org/10.1063/1.105889 (3 pages)

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A cathodoluminescence emission near 850 nm has been observed in GaAs/AlGaAs selectively doped heterostructures at room temperature which appears related to excitons confined to a two‐dimensional electron gas (2DEG). If the structure is grown without Si in the donor layer or if a top confining layer is removed, then this room temperature emission is not observed. At low temperatures (6 K) three peaks are observed at 797, 812, and 817 nm, in which the highest energy peak corresponds to the 850 nm room‐temperature emission. Both the low‐ and high‐energy peaks behave similarly with respect to variations in excitation intensity and temperature. A quadratic excitation dependence of the intensity indicates that these emissions are excitonic in origin. Both peaks exhibit quenching above ∼100 K with an activation energy of 0.11 eV, and the peak energies shift to higher energy as the temperature is lowered. While we attribute our 797 nm emission to excitons confined to a 2DEG in the well above the donor layer, the origin of the 817 nm peak is most likely related to excitons confined to the 2DEG in the 3000 Å buffer layer.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.60.Hk Cathodoluminescence, ionoluminescence
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