Maximum heat-sink temperature for CW operation of adouble-heterostructure semiconductor injection laser

Assuming that the temperature dependence of the threshold current for pulsed operation is known, an analytical expression for the maximum heat-sink temperature, T_hm, for CW operation of the laser can be derived. The maximum heat-sink temperature is expressed in terms of the characteristic temperature T₀, the room-temperature threshold current for pulsed operation I₀ , the equivalent effective thermal resistance &thetas;, and the equivalent effective series electrical resistance r of the device. It is shown that the values of T_hm can be enhanced by increasing the value of T₀ or by decreasing the values of I₀, &thetas;, and r     

Self-heating effects in basic semiconductor structures

Investigates the effects of self-heating on the high current I -V characteristics of semiconductor structures using a fully coupled electrothermal device simulator. It is shown that the breakdown in both resistors and diodes is caused by conductivity modulation due to minority carrier generation. In isothermal simulations with T=300 K, avalanche generation is the source of minority carriers. In simulations with self-heating, both avalanche and thermal generation of minority carriers can contribute to the breakdown mechanism. The voltage and current at breakdown are dependent on the structure of the device and the doping concentration in the region with lower doping. For all structures, except highly doped resistors with poor heating sinking at the contacts, the temperature at thermal breakdown ranged from 1.25T_i to 3T_i , where T_i is the temperature at which the semiconductor goes intrinsic. Hence, it is found that T=T_i is not a general condition for thermal (or second) breakdown. From these studies, an improved condition for thermal breakdown is proposed     

A model for fast switching transients in power systems: the nearzone concept

The author presents a simple time-domain model which makes it possible to predict the order of magnitude of the highest di/ dt values generated by closing switches in electrical power systems. The model is based on traveling-wave analysis. It is demonstrated that two different approaches must be applied, according to whether (a) the closing time, T_s, of the switch is faster than twice the traveling time to the first reflection point or (b) T_s is much slower. Under condition (b) the well-known quasistationary approach di/dt_max=U₀/L can be used, where U₀ is the switched voltage and L is the self-inductance of the line between the stray capacitances located to the left and the right of the switching device. Under condition (a) a new formula must be applied: di/dt _max≈2 U₀/ZT_s, where Z is the line impedance of the line in which the switching device is installed and T_s is the time during which the voltage across the switch collapses from U₀ to zero. Experimental results are given from both fast and slow closing switches     

High vibrational temperatures in optically-pumped CO2

A pulsed 4.3-μm CO₂ laser was used to optically pump mixtures of CO₂ and He, and create transient gain at 9 and 10 μm. A conventional continuous-wave CO₂ laser operating on both regular and sequence bands measures this transient gain, and determined the ν₃ (asymmetric stretching)-mode vibrational temperature T₃. The measured values of T ₃ are generally much higher than those attained in discharge-excited CO₂. It is shown that a Treanor distribution must be used to describe the populations in the ν₃ -mode when dilute mixtures of CO₂ in He are optically pumped to ν₃-mode temperatures of 3000 to 4000 K. Under these conditions the sequence-band gain coefficients are almost equal to those on the regular bands. The collisional relaxation of energy from the ν₃ mode shows evidence of fast V-T relaxation at high values of T₃, followed by a slower relaxation rate characteristic of the 00⁰1 population lifetime     

A fractal analysis of interconnection complexity

The emergent, collective properties of computer interconnections are shown to be characterized by a noninteger dimension D_i , which is, in general, different from the system's Euclidean dimension. This dimension characterizes the properties of a fractal support, or substrate, on which interconnections are placed to provide communication throughout the system. The interconnection support also acts as a host for a multifractal spectrum of interconnection distribution processes which characterize the change in connectivity in moving from the backplane to the transistor level. The properties of fractal systems are investigated by attempting to minimize their total wire length using a simulated annealing algorithm. Systems whose interconnection dimension is approximately equal to their Euclidean dimension are shown to possess minimum wire length arrangements. These results are then interpreted in terms of a geometrical temperature T _i=1/D_i. This analysis indicates that the system passes through a phase transition at T_i≈1/2 and that attainable system temperatures are bounded by 1/3⩽T_i⩽1. The consequences for simulated annealing are discussed     

Ultradry annealing after polysilicon electrode formation forimproving the TDDB lifetime of ultrathin silicon oxide films in MOSdiodes

Effects of ultradry annealing on time-dependent dielectric breakdown (TDDB) lifetime (T_TDDB) were investigated for Si MOS diodes with 5-nm-thick silicon oxide and P-doped polysilicon gate electrode films. This annealing was performed at 800°C in ultradry N₂ of less than 1-ppm moisture concentration after the electrode formation. Under an accumulation-bias stress condition, T_TDDB for the ultradry-annealed n-type Si diodes was larger than that for the conventionally annealed ones, while such T _TDDB enhancement was not confirmed in the p-type ones. Since positive charges induced near anode-side oxide interfaces are closely related to T_TDDB, the T_TDDB enhancement for the ultradry-annealed n-type Si diodes probably reflects a qualitative improvement of the anode-side, i.e., gate-electrode-oxide, interfaces by ultradry annealing     

The bandwidth performance of a two-element adaptive array withtapped delay-line processing

The bandwidth performance of a two-element adaptive array with a tapped delay line behind each element is examined. It is shown how the number of taps and the delay between taps affect the bandwidth performance of the array. An array with two weights and one delay behind each element is found to yield optimal performance (equal to that obtained with continuous-wave interference) for any value of intertap delay between zero and T₉₀/B, where T ₉₀ is a quarter-wavelength delay time and B is the fractional signal bandwidth. Delays less that T₉₀ yield optimal performance but result in large array weights. Delays larger than T₉₀/B yield suboptimal signal-to-interference-plus-noise ratio when each element has only two weights. For delays between T₉₀/B and 4T₉₀/B , the performance is suboptimal with only two taps but approaches the optimal if more taps are added to each element. Delays larger than T₉₀/B result in suboptimal performance regardless of the number of taps used     

Effect of conduction-band discontinuity on lasing characteristicsof 1.5 μm InGaAs/In(Ga)AlAs MQW-FP lasers

The characteristic temperature (T₀), relaxation frequency (f_r), differential gain (dg /dn) and nonlinear gain coefficient (ϵ) of 1.5-μm InGaAs/In(Ga)AlAs multiple-quantum-well (MQW) Fabry-Perot (FP) lasers grown by gas source molecular beam epitaxy (GSMBE) are reported. It is found that T₀ is little affected by the difference in the conduction band discontinuity. A maximum T₀ value of 86 K is obtained. The dg/dn and ϵ∈ were calculated from the slope of the f_r versus √ power plot and the damping K-factor. It is demonstrated that dg/dn and ϵ of InGaAs/In(Ga)AlAs MQW lasers increase with an increase in the conduction band discontinuity     

A new extrapolation algorithm for band-limited signals using theregularization method

The ill-posedness of the extrapolation problem in the presence of noise is considered. A stable algorithm is constructed by solving a Fredholm equation based on a regularization method. The algorithm appears relatively robust, since the noise η_δ(t ) is taken as a function in L²[-T,T](T>0) such that the error energy ∫|η_δ(t)|² dt⩽δ², where integration is from - T to T, and the constructed extrapolation uniformly converges to the desired signal over (-∞, +∞) as δ→0. An estimate for the error energy of the constructed extrapolation over (-∞, +∞) and for the absolute error between the constructed extrapolation and the desired signal over (-∞, +∞) are presented     

Strain-induced performance improvements in long-wavelength,multiple-quantum-well, ridge-waveguide lasers with all quaternary activeregions

A comparison between the performance of strained (1.5% compression) and unstrained multiple-quantum-well (MQW), ridge-waveguide lasers with identical geometrical structures and similar emission wavelengths is reported. Results show that significant improvements in the characteristic temperature (T₀), maximum output power, maximum operating temperature, and internal quantum efficiency can be obtained through the applications of strain. Accordingly, for lasers employing strained active regions, an improved characteristic temperature, T₀, of 85 K and high-maximum lasing temperature of 140°C were obtained under pulsed operating conditions. These values are the highest ever observed for long-wavelength lasers with all-quaternary strained MQW active regions     

Double-active-layer index-guided InGaAsP-InP laser diode

A buried crescent InGaAsP-InP laser with two active layers was fabricated to study the temperature behavior of the double-carrier-confinement structure. An anomalously high characteristic temperature T₀ was measured, and optical switching behavior was observed. A mode analysis and numerical calculation using a rate equation approach explained qualitatively very well the experimental results. It was revealed that both the Auger recombination in this special double-active-layer configuration and the temperature-dependent leakage current, which leads to uniform carrier distribution in both active regions, are essential to increase T₀     

Error performance of a digitally processed binary ESK frequencyhopping receiver in the presence of large Doppler

Analysis is made of the effects of Doppler on the error rate performance of a low data rate binary FSK frequency hopping receiver, employing a discrete Fourier transform (DFT) technique for baseband detection. Bit detection decision is made by locating the maximum of the DFT outputs which, in the frequency domain, are assumed to be separated by 1/T where T is the bit period. Both the worst case and average error performances are obtained and presented as a function of E_b/N₀ for various values of M where E_b/N₀ is the signal bit energy-to-noise density ratio and M is the degree of freedom associated with the Doppler uncertainty window. The E _b/N₀ degradation as a function of M is also presented     

The effects of source/drain resistance on deep submicrometer deviceperformance

As MOSFET channel lengths approach the deep-submicrometer regime, performance degradation due to parasitic source/drain resistance (R _sd) becomes an important factor to consider in device scaling. The effects of R_sd on the device performance of deep-submicrometer non-LDD (lightly doped drain) n-channel MOSFETs are examined. Reduction in the measured saturation drain current (R_sd=600 Ω-μm) relative to the ideal saturation current (R_sd=0.0 Ω-μm) is about 4% for L_eff=0.7 μm and T_ox =15.6 nm and 10% for L_eff=0.3 μm and T _ox=8.6 nm. Reduction of current in the linear regime and reduction of the simulated ring oscillator speed are both about three times higher. The effect of salicide technologies on device performance is discussed. Projections are made of the ultimate achievable performance     

Current-crowding effect in diagonal MOSFET's

Electrical and reliability characteristics of diagonally shaped n-channel MOSFETs have been extensively investigated. Compared with the conventional device structure, diagonal MOSFETs show longer device lifetime under peak I_sub condition (V_g =0.5 V_d). However, in the high-gate-bias region (V_g=V_d), diagonal MOSFETs exhibit a significantly higher degradation rate. From the I_sub versus gate voltage characteristics, this larger degradation rate under high gate bias is concluded to be due mainly to the current-crowding effect at the drain corner. For a cell-transistor operating condition (V_g>V_d), this current-crowding effect in the diagonal transistor can be a serious reliability concern     

Transient stimulated Raman scattering in lead vapor

An investigation of stimulated Raman scattering (SRS) of short-pulse (6-ns) XeCl-laser radiation in Pb vapor is reported. Conversion efficiencies, based on peak power, up to 15% have been obtained for Pb-oven temperatures of 1260°C. The functional dependence of conversion efficiency, in the short-pulse regime, upon buffer-gas pressure and species differs significantly from that observed for long-pulse (>20-ns) pumping, corresponding to steady state behavior. Analysis of the data and comparison with transient SRS in H ₂ yield an estimate of T₂≈1ns for the transient response time T₂ of Pb vapor. The observed pressure effects are explained in terms of a reduction in T₂, and hence Raman gain, by collisions with buffer-gas atoms     

The design and characterization of nonoverlapping superself-aligned BiCMOS technology

An optimal device structure for integrating bipolar and CMOS is described. Process design and device performance are discussed. Both the vertical n-p-n and MOS devices have non-overlapping super self-aligned (NOVA) structures. The base-collector and source/drain junction capacitances are significantly reduced. This structure allows complete silicidation of active polysilicon electrodes, cutting down the parasitic resistances of source, drain, and extrinsic base. The critical gate and emitter regions are protected from direct reactive ion etching exposure and damage. All shallow junctions are contacted by polysilicon electrodes which suppress silicide-induced leakage. An arsenic buried layer minimizes collector resistance and collector-substrate capacitance. A novel selective epitaxy capping technique suppresses lateral autodoping from the arsenic buried layer. Fully recessed oxide with polysilicon buffer layer is used to achieve a low defect density device isolation. CMOS with L_eff=1.1 μm and W _n/W_p=10 μm/10 μm exhibits averaged ring oscillator delay of 128 ps/stage. An n-p-n transistor with f_T, of 14 GHz and low-power emitter-coupled logic ring oscillator with a delay of 97 ps/stage have been fabricated     

A model for hot-electron-induced MOSFET linear-current degradationbased on mobility reduction due to interface-state generation

A simple model for the hot-electron degradation of MOSFET linear-current drive is developed on the basis of the reduction of the inversion-layer mobility due to the generation of interface states. The model can explain the observed dependence of the device hot-electron lifetime on the effective channel length and oxide thickness by taking into account both the relative nonscalability of the localized damage region and the dependence of the linear-current degradation on the effective vertical electric field E_eff. The model is verified for deep-submicrometer non-LDD n-channel MOSFETs with L_eff=0.2-1.5 μm and T_ox=3.6-21.0 nm. From the correlation between linear-current and charge-pumping degradation, the scattering coefficient α, which relates the number of generated interface states to the corresponding amount of inversion-layer mobility reduction, can be extracted and its dependence on E_eff determined. Using this linear-current degradation model, existing hot-electron lifetime prediction models are modified to account explicitly for the effects of L_eff and T _ox     

Noise performance at cryogenic temperatures at AlGaAs/InGaAs HEMT'swith 0.15-μm T-shaped WSix gates

T-shaped 0.15-μm WSi_x gate HEMTs have been fabricated on AlGaAs/InGaAs MBE wafers. Their S-parameters, output noise spectral density P_no, and noise temperatures T _e at cryogenic temperatures, were measured. The current gain cutoff frequency f_T increases from 61 GHz at 295 K to 87 GHz at 90 K. P_no and T_e measurements indicate that the hot-electron effect is noticeable at low temperatures at high drain current. At 30 GHz, the noise temperature is 19±3 K with an associated gain of 10.4 dB at the physical temperature of 20 K. The results demonstrate the great potential of AlGaAs/InGaAs HEMTs for low-temperature applications     

A closed-loop evaluation and validation of a method for determiningthe scattering limited carrier velocity in MOSFETs

A closed-loop evaluation of a saturation transconductance (g _msat⁽ⁱ⁾) based method for determining the scattering limited carrier velocity (ν_sat) in enhancement MOSFETs was performed with the use of a 2-D device simulator. Consistency in the extracted ν_sat over a wide range of gate oxide thickness (T_ox), channel doping concentration, and bias condition was tested and verified. Also analyzed are the appropriate measurement condition, the significance of the parasitic effect due to the source and drain resistances, the applicability of the method used for compensating this parasitic effect, and the expected accuracy of the extracted ν_sat under ideal conditions. A plausible explanation is provided for the inconsistency between ν_sat determined from g_msat⁽ⁱ⁾(0), the extrapolated transconductance, and ν_sat determined from the slope of [ g_msat⁽ⁱ⁾(0)]^-1 versus T _ox characteristics observed in published results. The g_msat ⁽ⁱ⁾-based method for extracting ν_sat has been applied to MOSFETs fabricated with three vastly different technologies, and the experimentally-based ν_sat of electrons at 300 K ranges from 7.37×10⁶ to 7.92×10⁶ cm/s, which shows its independence of technology     

On the semiconductor laser logarithmic gain-current densityrelation

The simplified relation, α=G₀ In (η _iJ/J₀), between material gain α and current density J is shown to be a very good shape approximation, for quantum wells and bulk materials, essentially independent of the type of recombination processes present. Simulations show that for a given material system, G₀ decreases by only about 30% from pure electron-hole-recombination-dominated to pure Auger-recombination-dominated. A generic quantum-well situation is explored to reveal the density of states and recombination coefficient dependence of G₀ and to formulate simple estimates for G₀. The results were tested against published data for eight quantum-well diode lasers. The predicted values of G ₀ were generally found to be in agreement with experiments only for the wider gap diodes. The discrepancies were attributed in part to carrier induced absorption, and it is shown that the formalism can be modified in selected cases to incorporate this without changing the basic form of the gain. A new expression which relates the temperature dependence of the measured parameters to the characteristic temperature, T₀, is provided