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13 Jun 1994

Volume 64, Issue 24, pp. 3205-3350

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Efficient laser performance of Nd3+:Sr5(PO 4)3F at 1.059 and 1.328 μm

X. X. Zhang, P. Hong, G. B. Loutts, J. Lefaucheur, M. Bass, and B. H. T. Chai

Appl. Phys. Lett. 64, 3205 (1994); http://dx.doi.org/10.1063/1.111337 (3 pages) | Cited 10 times

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High efficiency, low threshold laser performance of Nd3+ doped Sr5(PO4)3F, or S‐FAP, crystals has been demonstrated. Its performance and properties compared with commercially available Nd:YVO4 indicate that Nd:S‐FAP is an outstanding medium for diode pumped laser applications at both 1.059 and 1.328 μm.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.-v Laser optical systems: design and operation

Highly efficient blue light generation in KTiOPO4 waveguides

D. Eger, M. Oron, M. Katz, and A. Zussman

Appl. Phys. Lett. 64, 3208 (1994); http://dx.doi.org/10.1063/1.111338 (2 pages) | Cited 23 times

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Very high normalized efficiency, up to 800% W−1 cm−2 for infrared to blue light conversion (425 nm), has been obtained in quasi‐phase‐matched waveguides in KTiOPO4. It is shown by a detailed calculation that this value is higher by a factor of 4 than that predicted by theory.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Second‐harmonic generation in bulk and waveguided LiTaO3 with domain inversion induced by electron beam scanning

Mool C. Gupta, William Kozlovsky, and Alan C. G. Nutt

Appl. Phys. Lett. 64, 3210 (1994); http://dx.doi.org/10.1063/1.111339 (3 pages) | Cited 13 times

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Bulk quasi‐phase‐matched frequency doubling experiments are reported for a lithium tantalate crystal which was periodically poled through its 0.5 mm thickness by electron beam scanning. The measured phase‐matching bandwidth of 1 nm for the 2‐mm‐long domain inverted section was close to the theoretical value of 0.4 nm, although the conversion efficiency was lower than theoretically expected. Chemical etching revealed domain duty‐cycle variations and incomplete inversions which are likely to have caused the lower conversion efficiency. Frequency doubling in waveguides fabricated in this material produced a normalized conversion efficiency of 290%/W cm2 and a phase matching bandwidth of 0.3 nm for a 1‐mm‐long domain inverted region.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Single‐domain layers formed in heat‐treated LiTaO3

Henrik Åhlfeldt

Appl. Phys. Lett. 64, 3213 (1994); http://dx.doi.org/10.1063/1.111340 (3 pages) | Cited 9 times

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Ferroelectric single‐domain surface layers are formed in z‐cut LiTaO3 following heat treatment above the Curie temperature. The polarity of the layers is the same as the polarity of the previously observed domain‐inverted layers formed in heat‐treated LiNbO3. The physical mechanisms behind these two phenomena are believed to be closely related.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
81.40.Rs Electrical and magnetic properties related to treatment conditions

Analytical method for calculation of temperature distribution in laser‐irradiated media with an external cooled surface

Y. Gurevich, N. Filonenko, and N. Salansky

Appl. Phys. Lett. 64, 3216 (1994); http://dx.doi.org/10.1063/1.111973 (3 pages) | Cited 3 times

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A method of spatial temperature field calculation based on an approximate analytical solution is presented for laser‐induced heating in a light‐absorbing medium combined with surface cooling. Example calculations show how this approach can provide temperature field control and heating area localization within the irradiated medium. The concept can be useful for various applications, particularly in medicine.
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42.62.-b Laser applications
61.80.Az Theory and models of radiation effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
87.50.W- Optical/infrared radiation effects

InAs1−xSbx/In1−yGayAs multiple‐quantum‐well heterostructure design for improved 4–5 μm lasers

Z. L. Liau and H. K. Choi

Appl. Phys. Lett. 64, 3219 (1994); http://dx.doi.org/10.1063/1.111341 (3 pages) | Cited 7 times

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A new strained‐layer multiple‐quantum‐well (MQW) heterostructure comprising InAs1−xSbx wells and In1−yGayAs barrier layers is proposed for improved 4–5 μm lasers. Both well and barrier compositions are close to InAs and are potentially well suited for high‐quality crystal growth of MQWs on either InAs or GaSb substrates. Simple modeling shows favorable valence‐band alignment suitable for carrier confinement, free of the staggered band alignment problem generally found in the conventional designs. Perturbation calculation of the effect of the compressive strain in the wells also shows sufficient valence subband separation. This and the reduced hole mass are expected to considerably lower the threshold carrier density and Auger recombination.
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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
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Small‐signal modulation and temperature dependence of the tunneling injection laser

L. Davis, H. C. Sun, H. Yoon, and P. K. Bhattacharya

Appl. Phys. Lett. 64, 3222 (1994); http://dx.doi.org/10.1063/1.111342 (3 pages) | Cited 13 times

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Recently, we demonstrated a novel laser structure, called the tunneling injection laser, where the electrons are injected into the active lasing quantum well region via tunneling. High performance results for this device have now been demonstrated. A To of 160 K was found from temperature‐dependent measurements (25–70 °C). High differential gain (5.5×10−16 cm2) and modulation bandwidth (12.5 GHz) have been attained relative to other single quantum well lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation
73.40.Gk Tunneling

Read‐only optical disk with superresolution

Yihong Wu, Hock Khoo, and Takuyo Kogure

Appl. Phys. Lett. 64, 3225 (1994); http://dx.doi.org/10.1063/1.111316 (3 pages) | Cited 7 times

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The possibility of achieving superresolution in a read‐only optical disk system with modified disk structures was investigated by simulation. The disk differs from the existing disks (such as compact disk) in addition of bilayer semiconductor materials. The absorption coefficient (α) of the semiconductor materials near band edge can be approximated by α∝(hν−EG)1/2 with hν as the photon energy and EG the band gap. Since the band gap EG within a certain range above room temperature decreases almost linearly with increasing the temperature, a strong nonlinearity of transmittance can be obtained by choosing a proper combination of EG and wavelength of the readout light source. Simulation results reveal that the spacial cutoff frequency can be significantly increased by the nonlinear transmittance of the additional semiconductor layers near the band edge.
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42.79.Vb Optical storage systems, optical disks

Noncritical phase matching and photorefractive damage in Sc2O3:LiNbO3

Joyce K. Yamamoto, T. Yamazaki, and K. Yamagishi

Appl. Phys. Lett. 64, 3228 (1994); http://dx.doi.org/10.1063/1.111317 (3 pages) | Cited 12 times

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The noncritical phase‐matching temperature, Tpm, of Sc2O3‐doped LiNbO3 was measured as a function of Sc2O3 concentration (0.0, 0.5, 1.0, and 1.5 mol % Sc2O3). Increasing the Sc2O3 concentration increased the phase‐matching temperature, but to a lesser extent than reported in MgO:LiNbO3. The maximum phase‐matching temperature was 46.5 °C in the 1.0 mol % Sc2O3:LiNbO3 crystal with an estimated temperature bandwidth of 1° cm. Photorefractive damage, determined by distortion in the transmitted beam, decreased with increasing Sc concentration, reaching a damage level comparable to that observed in 5.0 mol % MgO:LiNbO3 crystal in the 1.5 mol % Sc2O3:LiNbO3 crystal.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
61.72.up Other materials

Structure and stability of sputter deposited beta‐tungsten thin films

I. A. Weerasekera, S. Ismat Shah, David V. Baxter, and K. M. Unruh

Appl. Phys. Lett. 64, 3231 (1994); http://dx.doi.org/10.1063/1.111318 (3 pages) | Cited 37 times

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The structure and stability of thin tungsten films prepared by radio frequency magnetron sputter deposition have been studied by x‐ray diffraction and x‐ray photoelectron spectroscopy. The structure of these films has been found to systematically evolve from the metastable A15 β‐W phase to the equilibrium A2 α‐W phase with decreasing oxygen impurity concentration. Within the β‐W phase a decrease in the concentration of incorporated oxygen results in a monotonic decrease in the lattice parameter of the unit cell until the β‐W phase eventually becomes unstable, and the α‐W phase is formed.
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81.15.Cd Deposition by sputtering
81.30.Bx Phase diagrams of metals, alloys, and oxides

Effects of dual spectral sources on the curing of polyimide films by rapid isothermal processing

M. A. Wait, J. Mavoori, R. Singh, J. E. Harriss, K. F. Poole, J. W. Kolis, R. P. S. Thakur, and A. A. Ogale

Appl. Phys. Lett. 64, 3234 (1994); http://dx.doi.org/10.1063/1.111320 (3 pages) | Cited 8 times

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There are fundamental differences between conventional furnace processing (CFP) and rapid isothermal processing (RIP). The radiation spectrum of a conventional furnace consists of photons in the infrared and longer wavelength regions, whereas the spectrum of the incoherent light sources used in RIP consists of some UV, visible, and infrared photons. As compared to CFP, the photophysical and photochemical effects associated with RIP provide the capability of lower temperature processing. However, a further reduction in processing temperature can be achieved by the use of vacuum ultraviolet (VUV) and UV light sources in conjunction with a single spectral source RIP. We provide experimental results for the dual spectral source curing of polyimide dielectric films. Our findings indicate that simultaneous exposure of polyimide samples to both VUV and conventional RIP sources during processing cured the polyimide more rapidly and at lower temperatures than did single spectral source RIP alone. These results may be of great importance for the RIP of the future generation of semiconductor devices.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light

Polyperinaphthalene film formation by pulsed laser deposition with a target of perylenetetracarboxylic dianhydride

M. Yudasaka, Y. Tasaka, M. Tanaka, H. Kamo, Y. Ohki, S. Usami, and S. Yoshimura

Appl. Phys. Lett. 64, 3237 (1994); http://dx.doi.org/10.1063/1.111321 (3 pages) | Cited 39 times

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Thin films of polyperinaphthalene (PPN) have been obtained by Nd:YAG pulsed laser deposition with a target of perylenetetracarboxylic dianhydride. Components of the films depend on the power and wavelength of the laser light, which is verified by absorption spectra, Raman scattering spectra, and in situ mass spectra. The optimum conditions for the PPN film formation is 10 mJ cm−2 at 266 nm.
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81.15.Fg Pulsed laser ablation deposition

Scanning tunneling microscopy observation of hydrogen‐terminated Si(111) surfaces at room temperature

K. Usuda, H. Kanaya, K. Yamada, T. Sato, T. Sueyoshi, and M. Iwatsuki

Appl. Phys. Lett. 64, 3240 (1994); http://dx.doi.org/10.1063/1.111297 (3 pages) | Cited 23 times

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Scanning tunneling microscopy has been applied to observe hydrogen‐terminated Si(111) surfaces at room temperature. A clear image was easily observed for a Si surface prepared by rinsing in pure water with very low dissolved oxygen after removal of native oxide by 1% HF solution dipping. A smooth surface in an atomic scale was exhibited in a 50×50 nm area. Completely triangular‐shaped holes were observed on the surface. The holes were surrounded by steps which were very likely directed toward 〈112〉. The treatment of the surface was remarkably stable even after a 3 h air exposure. Furthermore, nm size pits were found at the bottom part of the triangular‐shaped holes. The results imply that the nm size pits appeared to be due to microdefects and that the pits might be the origin of surface etching at the Si surface.
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81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Scanning tunneling microscopy using a ZnO whisker tip

T. Yoshida, H. Naito, M. Okuda, S. Ehara, T. Takagi, O. Kusumoto, H. Kado, K. Yokoyama, and T. Tohda

Appl. Phys. Lett. 64, 3243 (1994); http://dx.doi.org/10.1063/1.111298 (3 pages) | Cited 7 times

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A zinc oxide (ZnO) whisker crystal has been examined as a probing tip for scanning tunneling microscopy (STM). Atomic resolution images of the surfaces of highly oriented pyrolytic graphite and Si(111)‐7×7 structures are successfully observed by STM using a ZnO whisker tip, demonstrating that the ZnO whisker crystal is applicable to a STM tip.  
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Direct bonding of organic materials

G. A. C. M. Spierings and J. Haisma

Appl. Phys. Lett. 64, 3246 (1994); http://dx.doi.org/10.1063/1.111299 (3 pages) | Cited 7 times

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Direct bonding of polymethylmethacrylate (PMMA) is described as an example of the applicability of direct bonding to organic materials such as polymers. Direct bonding of a PMMA wafer to itself and to silicon and fused silica wafers is realized. At room temperature, the value of the bond energy indicates the presence of weak chemical interactions at the bonded interface. Heating a bonded PMMA/PMMA wafer pair to the glass transition temperature of PMMA (105 °C) and higher temperatures causes the two surfaces to fuse and the interface to become bridged by polymer chains.  
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Stress‐controlled silicon nitride film with high optical transmittance prepared by an ultrahigh‐vacuum electron cyclotron resonance plasma chemical‐vapor deposition system

Jinho Ahn and Katsumi Suzuki

Appl. Phys. Lett. 64, 3249 (1994); http://dx.doi.org/10.1063/1.111300 (3 pages) | Cited 10 times

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An ultrahigh‐vaccuum electron cyclotron resonance plasma chemical‐vapor deposition system with a substrate heating component has been applied to deposit silicon nitride film. Low background pressure (∼5×10−9 Torr) and efficient plasma excitation at a low deposition pressure (<10−3 Torr) result in a low oxygen impurity content in the silicon nitride film. Process flexibility of this system, i.e., control of the SiH4 to NH3 flow ratio, deposition pressure, and substrate temperature, allows the deposition of near‐stoichiometry silicon nitride film with a high optical transmittance as well as a suppressed amount of hydrogen impurity and a low film stress.  
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Nk Insulators

Growth of highly oriented ZrTiO4 thin films by radio‐frequency magnetron sputtering

De‐An Chang, Pang Lin, and Tseung‐Yuen Tseng

Appl. Phys. Lett. 64, 3252 (1994); http://dx.doi.org/10.1063/1.111947 (3 pages) | Cited 6 times

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ZrTiO4 thin films on Si(100), metals [Al, Ti and Pt coated on Si(100)] and glass were prepared by radio‐frequency magnetron sputter deposition. All films on crystalline substrates exhibited a highly preferred orientation in [020], which were evidenced by the full width at half‐maximum (≤0.046°) of the associated rocking curves. The structure of the films on glass, depending on the substrate temperature, was either amorphous or random polycrystalline. Good stoichiometric quality and thermal stability have been observed in films on silicon. The X‐ray diffraction and transmission electron microscopy selected‐area diffraction studies indicated that, after a sequence of annealing up to 650–700 °C, the distributions of Zr and Ti ions in the octahedral cation sites of crystal structure of the films remained disordered.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Heterogeneous ceramic system prepared from semiconducting compound InSb

M. Jergel, J. Červenák, V. Štrbík, and F. Hanic

Appl. Phys. Lett. 64, 3255 (1994); http://dx.doi.org/10.1063/1.111301 (3 pages)

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A cermet compact consisting of unreacted semiconducting InSb, semiconducting In2O3, and metallic Sb has been prepared by partial oxidation of polycrystalline bulk InSb at elevated temperatures in flowing oxygen. Unusually constant electric resistivity of this heterogeneous system has been observed in the temperature range from 4.2 to 300 K. Stability of the electric resistance depends on the degree of conversion β in the oxidation reaction: 2 InSb+3/2 O2=In2O3+2 Sb. Our thermogravimetric and x‐ray studies revealed an escape of Sb from the system at higher temperatures and longer reaction times. The initial polycrystalline InSb was prepared by the method of rapid quenching.
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81.05.Mh Cermets, ceramic and refractory composites
81.30.Dz Phase diagrams of other materials
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Electron distribution in a periodically line‐doped GaAs

Y. Takagaki, K. J. Friedland, and K. Ploog

Appl. Phys. Lett. 64, 3258 (1994); http://dx.doi.org/10.1063/1.111302 (3 pages) | Cited 2 times

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The electrostatic potential and the electron distribution in periodically wirelike Si‐doped GaAs are calculated within the semiclassical approximation for a distance between the wires of D=8–16 nm. It is shown that the mutual coupling between channels is significant for these wire separations. The electron distribution is most homogenized when the average electron density is ns∼5×1015 m−2, nearly independent of D. The existence of one‐dimensional bound states is found to be unlikely even for ns∼8×1016 m−2 when D=8 nm, indicating that the electron distribution modulation is sustained by two‐dimensional states.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors

Importance of collector doping in the design of AlInAs/GaInAs/InP double heterojunction bipolar transistors

M. Hafizi, T. Liu, W. E. Stanchina, D. B. Rensch, M. Lui, and Y. K. Brown

Appl. Phys. Lett. 64, 3261 (1994); http://dx.doi.org/10.1063/1.111303 (3 pages) | Cited 3 times

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AlInAs/GaInAs/InP double heterojunction bipolar transistors (DHBTs) have been made with an InP collector thickness of 0.75 μm and collector dopings of 1.4, 2.4, and 3×1016 cm−3. It is shown that because of the conduction band potential barrier between the GaInAs base and the InP collector in DHBTs and particular velocity‐field characteristics of InP, the dc and rf performance of the DHBT is very sensitive to the collector doping level. With a collector doping of 3×1016 cm−3 devices conducted a collector current density of 1×105 A/cm2 without gain compression and had a IC‐VCE saturation voltage of about 2 V. Base‐collector and collector‐emitter breakdown voltages were 22 and 14.5 V, respectively, and fT and fmax were in the range of 65–70 GHz.
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85.30.Pq Bipolar transistors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors

Oxidation enhanced dopant diffusion in separation by implantation by oxygen silicon‐on‐insulator material

S. W. Crowder, P. B. Griffin, C. J. Hsieh, G. Y. Wei, J. D. Plummer, and L. P. Allen

Appl. Phys. Lett. 64, 3264 (1994); http://dx.doi.org/10.1063/1.111304 (3 pages) | Cited 4 times

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An effective interstitial surface recombination velocity for the buried Si‐SiO2 interface in separation by implantation of oxygen (SIMOX) material has been used to accurately model the oxidation‐enhanced diffusion of boron and phosphorous in single‐ and multiple‐implant material. The effective recombination velocity at the SIMOX interface was found to be higher than the value for a thermally grown SiO2 interface. The enhancement of the effective recombination velocity is dependent on the material formation conditions and is empirically related to the near‐interface dislocation density. Increased surface interfacial area is considered to be the most likely cause for the increased effective recombination velocity.
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66.30.J- Diffusion of impurities
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Reflectivity measurements of femtosecond carrier and field dynamics in semiconductors

U. D. Keil, D. R. Dykaar, R. F. Kopf, and S. B. Darack

Appl. Phys. Lett. 64, 3267 (1994); http://dx.doi.org/10.1063/1.111305 (3 pages) | Cited 7 times

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Carrier and field dynamics in a photoconductive switch are investigated by voltage modulated reflectivity. Measurements are performed with single, femtosecond pulsed and cw probe beams, and with pulsed pump and probe beams. We investigate the spatial dependence of the reflectivity changes and show that for mode‐locked probe light the signal at the positive electrode completely dominates the response. The comparison of above and below bandgap excitation and reflectivity changes resolves the contributions of carrier‐induced field changes and those due to the modulation of the applied field. Photoconductive switches on p‐ and n‐doped substrates show that field enhancement at the Schottky barriers has only secondary influence. We explain the results in terms of a two‐dimensional field distribution which produces the largest field gradient and hence acceleration of carriers at the electrodes and that the higher mobility of electrons accounts for the dominant signal appearing at the positive electrode.
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78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Control of anomalous boron diffusion in the base of Si/SiGe/Si heterojunction bipolar transistors using PtSi

D.‐X. Xu, C. J. Peters, J.‐P. Noël, S. J. Rolfe, and N. G. Tarr

Appl. Phys. Lett. 64, 3270 (1994); http://dx.doi.org/10.1063/1.111306 (3 pages) | Cited 5 times

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In Si/SiGe/Si heterojunction bipolar transistor structures, very shallow arsenic implant on the emitter has been found to cause anomalous boron diffusion in the base. This phenomenon imposes stringent constraints on the device fabrication processes. We discovered that by using platinum silicide, which also served as a self‐aligned low resistance contact material to the emitter and base, the anomalous diffusion in the base was significantly reduced. In this letter, we report the experiment results, and propose possible explanations.
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85.30.Pq Bipolar transistors
66.30.J- Diffusion of impurities
61.72.uf Ge and Si

Indium and gallium p‐type doping of hydrogenated amorphous germanium thin films

F. Fajardo, D. Comedi, and I. Chambouleyron

Appl. Phys. Lett. 64, 3273 (1994); http://dx.doi.org/10.1063/1.111307 (3 pages) | Cited 1 time

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Hydrogenated amorphous germanium films have been p‐type doped with indium and gallium. The room‐temperature dark dc conductivity of the films has been found to change by several orders of magnitude within the studied dopant atomic concentration range (∼3×10−5 to ∼1×10−2). The conductivity change from n to p type for the more heavily doped materials indicates effective p‐type doping. The hydrogen content and the optical gap of the doped films, on the other hand, remain essentially unchanged with respect to the undoped material. For the most doped samples, signs of metallic segregation have been detected in the case of gallium doping. Metallic segregation is not apparent for indium‐doped samples.
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73.61.Jc Amorphous semiconductors; glasses
72.80.Ng Disordered solids
61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Temperature and carrier density dependence of mobility in a heavily doped quantum well

Mark H. Somerville, David R. Greenberg, and Jesús A. del Alamo

Appl. Phys. Lett. 64, 3276 (1994); http://dx.doi.org/10.1063/1.111308 (3 pages) | Cited 2 times

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Interest in heterostructure field‐effect transistors (HFETs) utilizing narrow, heavily doped channels motivates a study of mobility in heavily doped quantum wells. We have measured electron mobility as a function of carrier concentration and temperature in an In0.15Ga0.85As quantum well with a doping of ND=6×1012 cm−2. Mobility is found to rise significantly as the ratio of electron to impurity concentration increases. Even at T=300 K, μ climbs by nearly a factor of 2 as carrier concentration in the well is increased from 1×1012 to 5×1012 cm−2. The results agree qualitatively with recently published theoretical predictions, and suggest that device models utilizing constant mobility are not appropriate for HFETs using doped two‐dimensional channels.
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73.50.Dn Low-field transport and mobility; piezoresistance
85.30.Tv Field effect devices
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