T. P. Pearsall

GexSi1−x strained‐layer superlattice waveguide photodetectors operating near 1.3 μm

Properties of GexSi1−x strained‐layer p‐i‐n detectors, in which the strained‐layer superlattice itself was used as an absorption region, have been studied for the first time. These devices were grown on (100)Si by molecular beam epitaxy. Using waveguide geometry we have obtained internal quantum efficiencies on the order of 40% at 1.3 μm in superlattices with the Ge fraction x=0.6. The superlattice detectors show the frequency response bandwidth of over 1 GHz and uniformly excellent electrical characteristics for values of x as large as 0.8.

Enhancement- and depletion-mode p-channel Ge x Si 1-x modulation-doped FET's

We report enhancement- and depletion-mode p-channel modulation-doped field-effect transistors (FETs) in Si. Si/GexSi1-xheterostructures were grown by molecular-beam epitaxy (MBE) with one-dimensional confinement of holes at the heterostructure interfaces. Transconductances of 2.5 and 3.2 mS/mm were measured at 300 K for enhancement- and depletion-mode devices, respectively, in good agreement with transistor modeling predictions for p-channel devices using measured material parameters.

Avalanche gain in Ge x Si 1-x /Si infrared waveguide detectors

Avalanche gain in GexSi1-x/Si heterostructures photodiodes has been measured for the first time. Absorption of infrared radiation occurs in a GexSi1-x/Si strained-layer superlattice (SLS) which serves as a waveguide core, and the avalanche multiplication takes place in one of the Si-cladding layers. Multiplication factors as high as 50 have been obtained for a 1.1-µm wavelength response (x = 0.2). The external absolute sensitivity operating at a multiplication of 10 is 1.1 A/W at 1.3 µm for an uncoated device.

The band structure dependence of impact ionization by hot carriers in semiconductors: GaAs

Abstract We present the first systematic study of the dependence of impact ionization by electrons and holes upon the details of the electronic band structure. Our measurements, made in GaAs, establish the crucial role of the ionization threshold energy, and its location in the Brillouin zone, in determining the ionization rates. This relationship is apparent in the dependence of impact ionization rates on the temperature of the lattice, compositional changes for the alloy GaAs 1- x Sb x , and the orientation and strength of the electric field. The strong dependence of impact ionization upon specific features of the electronic band structure is a new principle which can be used to study the nature of electronic states in a wide variety of semiconductors through hot-carrier behavior.

An experimental determination of the effective masses for GaxIn1−xAsyP1−y alloys grown on InP

The band‐edge effective mass for conduction electrons in GaxIn1−xAsyP1−y has been determined for several different alloy compositions covering the complete range of alloys grown lattice‐matched on InP. Measurements show that the effective mass varies nearly linearly with alloy composition.

Ge0.6Si0.4 rib waveguide avalanche photodetectors for 1.3 μm operation

Performance of strained‐layer superlattice Ge0.6Si0.4 waveguide avalanche photodetectors is evaluated for optical fiber applications at 1.3 μm. These devices are grown on Si substrates by molecular beam epitaxy. Waveguiding is accomplished by means of a 1.5–1.8‐μm‐thick Si rib waveguide which provides an effective index step of δn=8×10−3. The detector response bandwidth exceeds 8 GHz at a gain of 6. A receiver sensitivity of ηP=−29.4 dBm has been obtained at the data rate of 800 Mb/s with the corresponding error‐free transmission over 45 km of single mode fiber.

Single longitudinal‐mode optical phonon scattering in Ga0.47In0.53As

We show that only one of the four Raman active modes in Ga0.47In0.53As shows the required symmetry behavior for longitudinal optical (LO) phonons. An additional mode previously supposed to be LO shows mixed‐mode behavior and may be disorder activated. Our results prove that only one phonon mode in Ga0.47In0.53As is active in scattering electronic carriers, and thus in determining both electron and hole mobilities.

Efficient lattice‐matched double‐heterostructure LED’s at 1.1 μm from GaxIn1−xAsyP1−y

The growth and operation of lattice‐matched double‐heterostructure InP/Ga0.17In0.83As0.34P0.66/InP light‐emitting diodes is reported. These diodes have an emission wavelength of 1.1 μm and quantum efficiencies of 4%.

Measurement of the Γ‐L separation in Ga0.47In0.53As by ultraviolet photoemission

We have studied the valence band of Ga0.47In0.53As by ultraviolet photoemission using photon energies of 11.7, 16.8, and 21.2 eV. The photo‐electron energy spectra show that the valence band of Ga0.47In0.53As has well‐defined structure similar to that of binary III‐V semiconductors. We have used these spectra to determine a conduction band Γ‐L separation of 0.55 eV at 300 K.

Waveguide infrared photodetectors on a silicon chip

A novel infrared (IR) photodetector structure is discussed. It represents a waveguide in which the core is a strained-layer GexSi1-x/Si superlattice (SLS) sandwiched between Si layers of a lower refractive index. Absorption of infrared radiation occurs in the core region due to interband electron transitions, and photogenerated carriers are collected in the Si cladding layers. Due to the recently discovered effect of bandgap narrowing by the strain in alloy layers the fundamental absorption threshold of the SLS is shifted to longer wavelengths, so that the detector can be operated in the range of silica-fiber transparency, 1.3-1.55 µm. The optimum SLS composition and thickness have been estimated from the known material properties and waveguide theory. The detector quantum efficiency grows with the optical path length, remaining consistent with the requirements of high-speed fiber-optical communications. A major advantage of the proposed structure is the possibility of obtaining avalanche gain in the silicon cladding. First experimental results have demonstrated the validity of the concept.