Dual-wavelength (GaAl)As laser

A monolithic structure integrating two stripe-geometry (GaAl)As lasers emitting at 8500 and 8850 ? is described. The threshold currents for both lasers are in the 50?70 mA range. The spacing between the stripes for the device reported here is 25 ?m; it can be reduced to 10 ?m in order to optimise the direct coupling to a 50 ?m diameter fibre.     

High-frequency radiation intensity noise spectrum of c.w.d.h. GaAlAs-diode lasers

Measurements of the intrinsic intensity noise spectrum of the radiation from c.w.d.h. GaAlAs-diode lasers at different pump currents are reported. The intensity noise spectrum was measured in the frequency range from 30 MHz to 8 GHz. Operating temperatures of the lasers were 10°C and ?20°C. Stabilisation of the intensity fluctuations at currents above threshold seems to be effective at frequencies up to 8 GHz. The results are compared with computer solutions for a simple, analytical laser-noise model. A good qualitative agreement between measurements and theoretical predictions is found.     

Externally linear current amplifiers

This paper describes a method to implement externally linear internally non-linear (ELIN) current amplifiers. Two novel schemes of ELIN current amplifier circuits are proposed, including hyperbolic sine (SINH) and hyperbolic tangent (TANH) circuits. The obtained linear input-current ranges of SINH and TANH circuits are 400?µA_p-p with total harmonic distortion (THD) less than 2% and 140?µA_p–p with THD less than 0.2%, respectively, both at the input frequency 1?kHz. Also, the current gains of the proposed circuits can be varied either in positive or negative region by adjusting the dc bias currents. Their current gains are tunable in the range of ?10?A/A to 10?A/A and insensitive to temperature. Simulation results show that the performance of the circuits are as good as expected.     

InGaAsP/InGaAs heterojunction p-i-n detectors with low dark current and small capacitance for 1.3?1.6 ?m fibre optic systems

A new long wavelength p-i-n photodetector, consisting of an In0.53 Ga0.47 As absorbing layer and an adjacent InGaAsP p-n junction is demonstrated. These diodes exhibit dark currents as low as 0.2 nA and a capacitance < 0.5 pF at ? 10 V for a device area of 1.3 × 10?4 cm2. The external quantum efficiency is ? 60% at ? = 1.3 ?m for front illumination. A systematic study of the background doping of the quaternary layers using different InP sources is also reported.     

Low dark current GaAs/AlAs graded-parameter superlattice PIN photodetector

Preliminary measurements of the photoresponse of a GaAs p-n junction containing an undoped asymmetric GaAs/AlAs superlattice are presented. Very low reverse-bias dark currents (<6×10?8 A/cm2 at 3 V) are measured, while still retaining the speed and spectral response of a conventional GaAs PIN diode. The ?3 dB bandwidth is found to be greater than 1 GHz, and the responsivity is 0.1 A/W.     

Optical fibre Faraday rotation current sensor with closed-loop operation

A novel closed-loop fibre-optic current sensor based on the Faraday effect is described which maintains a constant sensitivity to AC currents in the presence of large quasi-DC and low-frequency current fluctuations. A Verdet constant of 2.55×10?6 rad/A (at 0.83 ?m) is reported for the fibre used.     

Experimental realisation of a full adder by substrate fed threshold logic structure

A full adder has been designed and fabricated utilising substrate fed threshold logic. The internal operation is performed by four-valued threshold currents while the input and output signals are of binary form. The delay times of the experimental circuit operating with 10 ?A per injection window have been measured as 5 ?s for the sums and 1 ?s for the carry.     

On the direct currents through interface states in metal-semiconductor contacts

The direct currents through interface states in metal-semiconductor majority-carrier contacts are calculated analytically. A transition is observed with forward bias voltage from metal-controlled to semiconductor-controlled occupancy of the interface states. Calculations for the Au-n-type silicon system indicate that interface state currents are comparable with band currents for densities ? 10¹¹ cm^?2 eV^?1 (oxide thickness 15 Å) or 10¹³ cm^?2 eV^?1 (10 Å).     

Leakage factor and burst noise in transistor arrays

Investigation of 4-transistor arrays in which the devices are very well matched at emitter currents above 100 nA has revealed correlation between burst noise and the departure from `matchness? at lower currents. A figure of merit based on the leakage currents ICBO,ICEO is introduced to compare individual devices and arrays.     

Frequency stabilisation of a reflex-klystron oscillator by a superconducting cavity

A powerful X band oscillator is reported, with a frequency stability comparable to a quartz clock of high quality. It is realised by coupling externally a standard reflex klystron 2K 25 to a high-Q factor (108) superconducting cavity. The observed frequency standard deviations in one second (10?10 in relative value) are in accordance with the theory.     

High-performance avalanche photodiode with separate absorption `grading? and multiplication regions

High-speed operation of avalanche photodiodes with separated absorption and multiplication regions has been achieved by incorporating an intermediate bandgap InGaAsP `grading? layer between the InP multiplication layer and the InGaAs absorption layer. These APDs also exhibit low dark currents, high quantum efficiencies and good avalanche gains. Sensitivity measurements have been made at 1.3 ?m and 1.55 ?m with one of these APDs in a high-speed optical receiver: at bit rates of 420 Mbit/s and 1 Gbit/s the minimum average powers required for 10?9 BER are ?43 dBm and ?38 dBm at 1.55 ?m, and ?41.5 dBm and ?37.5 dBm at 1.3 ?m, respectively.     

1.3 ?m InGaAsP DCPBH multiquantum-well lasers

We report the fabrication and performance characteristics of InGaAsP double-channel planar buried heterostructure (DCPBH) lasers with multiquantum-well active layers emitting at 1.3 ?m. These lasers have threshold currents in the range 40?50 mA at 30°C, external differential quantum efficiencies of ?50% at 30°C and T0 values ?160 to 180 K in the temperature range 10?60°C.     

High-speed 1.55 ?m single-longitudinal-mode ridge waveguide C3 laser

Fundamental-transverse-mode ridge waveguide laser chips were recleaved to form C3 lasers with a single-longitudinal-mode output stabilised at a fixed wavelength over a wide range of drive currents and temperature. Lasers operated at 1.55 ?m at a bit rate of 2 Gbit/s with on-off ratios greater than 10:1 and side-mode suppression greater than 1200:1. A simple method for mapping the stable operating regime is described.     

Low-leakage InGaAs photodiodes grown on gaAs substrates using a graded strained-layer superlattice

InxGa1?xAs layers with In concentrations up to 35% have been grown on GaAs substrates by MOCVD using a GaAs/InxGa1?xAs superlattice with graded layer thicknesses to accommodate the lattice mismatch. 105 ?m-diameter PIN diodes fabricated from this material have leakage currents below 1 nA at ? 10 V, comparable to devices from lattice-matched material on InP substrates.     

Luminescence spectra and efficiency of GaN-based quantum-well heterostructure light emitting diodes: Current and voltage dependence

Luminescence spectra and quantum yield in light emitting diodes (LEDs) based on InGaN/AlGaN/GaN heterostructures with multiple quantum wells (MQWs) were studied in the range of currents J=10⁻⁶–10⁻¹ A. Minor spread in the quantum yield at operating currents (±15% at J≈10 mA) was observed in these LEDs, which were fabricated by Hewlett-Packard. The spread is due to differences in the current and voltage dependences of the diode emission intensity, caused by differences in the charged center distribution across the space-charge region (SCR) of the structures and in the role of the tunnel current component at low voltages. In the diodes with a thin (≲120 nm) SCR, a tunnel emission band was observed for J≲100 μA; the peak energy of this band ℏω_max=1.92–2.05 eV corresponds to the voltage applied. At low currents (J=0.05–0.5 mA), the spectral position of the main peak ℏω_max=2.35–2.36 eV is independent of the voltage and is determined by the radiative transitions between the localized states. At J>1 mA, this band shifts with the current (ℏω_max=2.36–2.52 eV). Its shape corresponds to the model for the occupation of states in the two-dimensional energy band tails, which are caused by the microscopic potential fluctuations. The four parameters in this model are related to the calculated energy band diagram of the MQW structure. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 7, 2001, pp. 861–868. Original Russian Text Copyright ? 2001 by Kudryashov, Mamakin, Turkin, Yunovich, Kovalev, Manyakhin. Part of this study was reported at the 3rd All-Russia Workshop on Structures and Devices Based on Gallium, Indium, and Aluminum Nitrides (Moscow State University, 1999); the 3rd International Conference on Nitride Semiconductors (Montpellier, 1999); and the 4th European Gallium Nitride Workshop (Nottingham, 2000).     

The low-power-drain microelectronic VHF amplifier

Low-power-drain VHF amplifiers have some unique characteristics when they are miniaturized. And, if the design is special?requiring tight tolerances or intended for limited-quantity production?it is often desirable to make the RF micropower circuits from discrete components. Described in this article are the first-order device requirements and circuit considerations for such VHF amplifiers incorporating bipolar transistors operating at collector currents as low as 25 ?A. Two specific designs are offered, along with information pertinent to their construction.     

Current divider: a new negative feedback element for integrated amplifiers

A multistage small-signal amplifier is described having, instead of resistors, a current divider in the negative-feedback pad. The current divider is a transistor which has two collectors with very different current gains. In spite of not using any passive components, linear and stable amplification has been achieved, down to input currents of 10?11 A.     

1.5-V CMOS exponential current generator

A new low-voltage CMOS exponential current generator is proposed in this work. MOS transistors in weak-inversion region and a master?Cslave technique for the temperature compensation were used. The circuit was fabricated with standard CMOS 0.35???m process using a single supply voltage of 1.5?V. Experimental results validate the theoretical analysis and verify the effectiveness of the proposed structure. A 40?dB range linearly in dB controlled output current with less than 1.5?dB linearity error was achieved. The structure features ±1 and ±3?dB deviations for ±10% supply voltage and 80°C temperature variations, respectively.     

Low-threshold, high-power zero-order lateral-mode DQW-SCH metal-clad ridge waveguide (AlGa)As/GaAs lasers

Metal-clad ridge waveguide (MCRW), double quantum well, separately confined heterostrucuture (DQW-SCH) lasers have been fabricated having continuous-wave (CW) threshold currents of 10?12 mA and external differential quantum efficiencies of 41?46% per uncoated facet. Light/current characteristics are linear to >70 mW, and zero-order lateral mode operation was measured at 56 mW. The CW burn-off power density is nearly double the best previously reported value.     

Dynamic characteristics of double-barrier nanostructures with asymmetric barriers of finite height and widths in a strong ac electric field

The theory of the interaction of a monoenergetic flow of injected electrons with a strong high-frequency ac electric field in resonant-tunneling diode (RTD) structures with asymmetric barriers of finite height and width is generalized. In the quasi-classical approximation, electron wavefunctions and tunneling functions in the quantum well and barriers are found. Analytical expressions for polarization currents in RTDs are derived in both the general case and in a number of limiting cases. It is shown that the polarization currents and radiation power in RTDs with asymmetric barriers strongly depend on the ratio of the probabilities of electron tunneling through the emitter and collector barriers. In the quantum mode, when δ = ? ? ? _r = ?ω ? Γ (? is the energy of electrons injected in the RTD, ? is Planck’s constant, ω is the ac field frequency, ? _r and Γ are the energy and width of the resonance level, respectively), the active polarization current in a field of E ≈ 2.8?ω/ea (e is the electron charge and a is the quantum-well width) reaches a maximum equal in magnitude to 84% of the direct resonant current, if the probability of electron tunneling through the emitter barrier is much higher than that through the collector barrier. The radiation-generation power at frequencies of ω = 10¹²–10¹³ s^?1 can reach 10⁵–10⁶ W/cm² in this case.