The inhibition of negative resistance dipole waves and domains in n-GaAs

Expressions describing the growth and propagation of infinitesimal space-charge waves in the presence of a differential negative resistance are derived, and conditions for the inhibition of dipole waves and domains inn-GaAs of resistivity greater than 10Ω-cm at 300°K are obtained. Thermoelectric effects are estimated and found to be small for carrier densities much less than 10¹⁵cm^-3. Taking the negative differential resistivity to be larger than the ohmic resistivity by a factor of 10²leads to 1) condition for inhibition of dipole waves:nl^{2} lsim 10^{9}cm^-12) condition for inhibition of stable domains:nl lsim 10^{12}cm^-2whenn= electron density andl= specimen length. The relevance of these results to explaining the phenomena observed in amplifying crystals is pointed out. It is suggested that the condition for amplification is(frac{10^{9}}{n})^{1/2} lsim l lsim frac{10^{12}}{n}.     

The performance of an iris-loaded planar phased-array antenna of rectangular waveguides with an external dielectric sheet

A new method for calculating the performance of an iris-loaded planar phased-array antenna of rectangular waveguides is presented. The method is based upon the expansion of the tangential electric aperture field in terms of judiciously chosen functions. Also, the influence of a dielectric sheet in front of an antenna the apertures of which are loaded with inductive irises is investigated. In the experiments, a sheet with a low relative permittivity (epsilon_{r} = 2.3orepsilon_{r} = 3.5) is spaced in front of a space-fed planar antenna of some 850 radiating elements, and the total transmitted power of the antenna is measured as a function of frequency and scan angle. The results indicate, that both in theory and in practice, an excellent match can be achieved with a polythene sheet (epsilon_{r} = 2.3) or a Perspex sheet (epsilon_{r} = 3.5).     

Gain spectra in GaInAsP/InP proton-bombarded stripe-geometry DH lasers

We have measured gain spectra for TE polarization in a GaInAsP/InP laser as a function of dc bias current below laser threshold. The measurements were made on a low-threshold device with a stripe geometry defined by proton bombardment. A number of other characteristics of this and similar devices from the same wafer are also reported. These data permit the maximum gain coefficient of the active layer gmaxto be evaluated as a function of nominal current density Jnom. We obtain the linear relationshipg_{max} = (3.1 times 10^{-2}/eta_{r})(J_{nom} - eta_{r} 5.4 times 10^{3}), where ηris the radiative quantum efficiency. Our data apply only for large gain (g gsim 150cm^-1) and large Jnombecause the active layer of the test device is thin (0.1 μm).     

Opto-elastic constant in single mode optical fibers

The dependence of the photo-elastic (or opto-elastic) constant upon the relative refractive index difference, the normalized frequency, and the wavelength for single-mode optical fibers has been investigated. From experimental results, it is found that the opto-elastic constant strongly depends upon wavelength, but not upon the relative refractive index difference or normalized frequency. The measured values of the opto-elastic constant at 1.30 and 1.50 μm are(3.17 pm 0.03) times 10^{-5}(mm²/kg) and(3.08 pm 0.02) times 10^{-5}(mm²/kg), respectively.     

Higher dimensional orthogonal designs and applications

The concept of orthogonal design is extended to higher dimensions. A properg-dimensional design[d_{ijk cdots upsilon}]is defined as one in which all parallel(g-1)-dimensional layers, in any orientation parallel to a hyper plane, are uncorrelated. This is equivalent to the requirement thatd_{ijk cdots upsilon} in {0, pm x_{1}, cdots , pm x_{t} }, wherex_{1}, cdots , x_{t}are commuting variables, and thatsum_{p} sum_{q} sum_{r} cdots sum_{y} d_{pqr cdots ya} d_{pqr cdots yb} = left( sum_{t} s_{i}x_{i}^{2} right)^{g-1} delta ab,where(s{1}, cdots , s{t})are integers giving the occurrences ofpm x_{1}, cdots , pm x_{t}in each row and column (this is called the type(s_{1}, cdot ,s_{t})^{g-1})and(pqr cdots yz)represents all permutations of(ijk cdots upsilon). This extends an idea of Paul J. Shlichta, whose higher dimensional Hadamard matrices are special cases withx_{1}, cdots , x_{t} in {1,- 1}, (s_{1}, cdots, s_{t})=(g), and(sum_{t}s_{i}x_{i}^{2})=g. Another special case is higher dimensional weighing matrices of type(k)^{g}, which havex_{1}, cdots , x_{t} in {0,1,- 1}, (s_{1}, cdots, s_{t})=(k), and(sum_{t}s_{i}x_{i}^{2})=k. Shlichta found properg-dimensional Hadamard matrices of size(2^{t})^{g}. Proper orthogonal designs of type     

Further classifications of codes meeting the Griesmer bound (Corresp.)

For any(n, k, d)binary linear code, the Griesmer bound says thatn geq sum_{i=0}^{k-1} lceil d/2^{i} rceil, wherelceil x rceildenotes the smallest integergeq x. We consider codes meeting the Griesmer bound with equality. These codes have parametersleft( s(2^{k} - 1) - sum_{i=1}^{p} (2^{u_{i}} - 1), k, s2^{k-1} - sum_{i=1}^{p} 2^{u_{i} -1} right), wherek > u_{1} > cdots > u_{p} geq 1. We characterize all such codes whenp = 2oru_{i-1}-u_{i} geq 2for2 leq i leq p.     

Investigation of the lateral turn-on process of thyristors with an epitaxial p-base

In this paper, the effect of the p-base doping concentration NAon the spreading velocity vsin power thyristors is examined. Chemical vapor deposition (CVD) techniques are used to produce the p-base layer, in order to change the p-base doping concentration and thickness independently. The results show a large reduction of vswith growing p-base doping concentration. At a doping concentration higher than 5 × 10¹⁶/cm³the spreading velocity follows a power law with an exponent of -0,9. The introduction of a sandwiched low-doped player between the p⁺-base and the n-emitter slows down the plasma propagation. The decrease of vs, in both cases, is attributed to the reduction of the current gain β2of the n-p-n transistor with doping concentration. In order to explain this behavior, a simple expression for the spreading velocity is derived, which relates the spreading velocity to the time constant of current rise trand consequently to the feedback loop gain (β1β2) of the two transistor components. In this derivation, only the lateral drift current in the p-base is taken into account. It was found that vsis given byv_{s} sim 1/t_{r} sim ln beta_{1}beta_{2}, in good agreement with the experiment.     

On certain projective geometry codes (Corresp.)

LetVbe an(n, k, d)binary projective geometry code withn = (q^{m}-1)/(q - 1), q = 2^{s}, andd geq [(q^{m-r}-1)/(q - 1)] + 1. This code isr-step majority-logic decodable. With reference to the GF(q^{m}) = {0, 1, alpha , alpha^{2} , cdots , alpha^{n(q-1)-1} }, the generator polynomialg(X), ofV, hasalpha^{nu}as a root if and only ifnuhas the formnu = i(q - 1)andmax_{0 leq l < s} W_{q}(2^{l} nu) leq (m - r - 1)(q - 1), whereW_{q}(x)indicates the weight of the radix-qrepresentation of the numberx. LetSbe the set of nonzero numbersnu, such thatalpha^{nu}is a root ofg(X). LetC_{1}, C_{2}, cdots, C_{nu}be the cyclotomic cosets such thatSis the union of these cosets. It is clear that the process of findingg(X)becomes simpler if we can find a representative from eachC_{i}, since we can then refer to a table, of irreducible factors, as given by, say, Peterson and Weldon. In this correspondence it was determined that the coset representatives for the cases ofm-r = 2, withs = 2, 3, andm-r=3, withs=2.     

Solid-phase epitaxial Pd/Ge ohmic contacts to In1-xGaxAsyP1-y/InP

A Pd/Ge metallization to InGaAsP/InP semiconductors, formed with solid-phase epitaxy (SPE) technique, has been investigated in this study. With this method, ohmic contacts with low specific contact resistance (rho_{c} approx 2.3 times 10^{-6}Ω.cm²) have been achieved on p-type In0.53Ga0.47As(p approx 1.8 times 10^{19}/cm³). The same contact scheme also gives low specific contact resistance (rho_{c} approx 6 times 10^{-7}Ω.cm²) on n-type In0.53Ga0.47As (n approx 1.0 times 10^{19}/cm³). Excellent surface morphology is observed in all the samples, and the contacts do not deteriorate for at least 4 h at temperatures between 300 and 500°C.     

Dual product constructions of Reed - Muller type codes (Corresp.)

Various linear and nonlinearR(r,m)codes having parameters(2^{m}, 2^{k}, 2^{m-r})withk=sum_{i=0}^{r}left(^{m}_{i}right)are constructed fromR(r,q)andR(r,p)codes,m=p+q. A dual construction forR(m-r,m)codes fromR(p-r,p)andR(q-r,q)codes is also presented,m=p+q. As a simple corollary we have that the number of nonequivalentR(r,m)codes is at least exponential in the length (forr>1). ForR(m-r,m)codes, the lower bound is doubly exponential in the length (forr>1).     

Optimum low-level injection efficiency of silicon transistors with shallow arsenic emitters

The influence of As surface concentration CSEon the emitter efficiency βγand the temperature dependence of βγare reported. The theoretical model that is used to explain the variation of βγwith CSEis based upon the difference in the effective energy bandgaps in the emitter and base regionsDeltaE_{g}. Experimental measurements ofDeltaE_{g}versus CSEare presented. Measurements of βγversus CSEshow that the effective emitter doping densityQ_{E}/x_{eb}reaches a maximum value atC_{SE} cong 1.5 times 10^{20}atoms/cm³, corresponding to the threshold above whichDeltaE_{g} > 0. For the case of a constant active base doping/cm²QB, this also corresponds to an optimum in the emitter efficiency βγ. However, it is shown that in typical sequential diffusion processing of transistors, βγincreases monotonically with CSEbecauseQ_{B} = Q_{B}(C_{SE})decreases. In addition, for devices fabricated in this study,Deltabeta_{gamma}/DeltaC_{SE}atC_{SE}=2 times 10^{20}atoms/ cm³for As-diffused emitters (doped oxide) was ≈ 5 times greater than for ion-implanted-diffused As emitters, showing the superiority of implantation in controlling gain. Finally, transistors that were made withC_{SE} siml 1.4 times 10^{20}atoms/cm³(DeltaE_{g} = 0) showed βgamma(85°C)/ βγ(-15°C) ≤ 1.05.     

Absorption in the near-ultraviolet wing of the Kr2F*(410 nm) band

An intracavity laser technique has been used to study the absorption of electron-beam pumped Ne/Kr/F2gas mixtures (196 and 300 K) in the "blue wing" of the Kr2F emission continuum. The experiments were conducted at 358 nm using theupsilon' = 0 rightarrow upsilon" = 1transition of the N2(C rightarrow B) laser. Comparing the results with the predictions of a computer model, the species primarily responsible for absorption have been identified as Ne+2, Kr+2, and Kr2F*. The photoabsorption cross sections for Ne+2and Kr2F (Kr+2F-) at 358 nm have been estimated to be8.1 cdot 10^{-19}and5.4 cdot 10^{-18}cm², respectively. The Kr2F* absorption cross section is roughly 20 percent of that reported for Kr+2at the same wavelength. The fluorescence efficiency of Kr2F* ine-beam excited 94.93 percent Ne/5 percent Kr/0.07 percent F2(P_{total} = 4000torr) gas mixtures has been found to be a factor of 2.8 higher than that of the N2(C rightarrow B) band in Ar/5 percent N2mixtures. Also, the rate constant for quenching of Kr2F* by F2was measured to be(4.1 pm 0.5) cdot 10^{-10}cm³. s^-1at 300 K and(3.0 pm 0.5) cdot 10^{-10}cm². s^-1at 196 K.     

Second-harmonic generation in CDA and CD*A

Efficient second-harmonic generation at 5321 Å has been achieved in CDA and CD*A. At 50-MW pump power, loss-free peak power-conversion efficiency of 57 percent and 45 percent were obtained in CDA and CD*A, respectively, The nonlinear optical constant, corrected for multimode fluctuations, was found to bed_{36}(CDA) = d_{36}(CD*A) = (0.96 pm 0.11) times 10^{-9}ESU, which corresponds tod_{36}(CDA) = d_{36}(CD*A) = 0.92 times d_{36}(KDP). In addition, the temperature variation of the birefringenced(n_{2}^{e} - n_{1}^{o})/dThas been measured to be(8.0 pm 0.2) times 10^{-6}degC^-1for CDA and(7.8 pm 0.2) times 10^{-6}degC^-1for CD*A.     

An approximation to the weight distribution of binary primitive BCH codes with designed distances 9 and 11 (Corresp.)

Recently Kasami {em et al.} presented a linear programming approach to the weight distribution of binary linear codes [2]. Their approach to compute upper and lower bounds on the weight distribution of binary primitive BCH codes of length2^{m} - 1withm geq 8and designed distance2t + 1with4 leq t leq 5is improved. From these results, the relative deviation of the number of codewords of weightjleq 2^{m-1}from the binomial distribution2^{-mt} left( stackrel{2^{m}-1}{j} right)is shown to be less than 1 percent for the following cases: (1)t = 4, j geq 2t + 1andm geq 16; (2)t = 4, j geq 2t + 3and10 leq m leq 15; (3)t=4, j geq 2t+5and8 leq m leq 9; (4)t=5,j geq 2t+ 1andm geq 20; (5)t=5, j geq 2t+ 3and12 leq m leq 19; (6)t=5, j geq 2t+ 5and10 leq m leq 11; (7)t=5, j geq 2t + 7andm=9; (8)t= 5, j geq 2t+ 9andm = 8.     

Weight enumerator for second-order Reed-Muller codes

In this paper, we establish the following result. Theorem:A_i, the number of codewords of weightiin the second-order binary Reed-Muller code of length2^mis given byA_i = 0unlessi = 2^{m-1}or2^{m-1} pm 2^{m-l-j}, for somej, 0 leq j leq [m/2], A_0 = A_{2^m} = 1, and begin{equation} begin{split} A_{2^{m-1} pm 2^{m-1-j}} = 2^{j(j+1)} &{frac{(2^m - 1) (2^{m-1} - 1 )}{4-1} } \ .&{frac{(2^{m-2} - 1)(2^{m-3} -1)}{4^2 - 1} } cdots \ .&{frac{(2^{m-2j+2} -1)(2^{m-2j+1} -1)}{4^j -1} } , \ & 1 leq j leq [m/2] \ end{split} end{equation} begin{equation} A_{2^{m-1}} = 2 { 2^{m(m+1)/2} - sum_{j=0}^{[m/2]} A_{2^{m-1} - 2^{m-1-j}} }. end{equation}     

A new class of codes meeting the Griesmer bound

An infinite sequence ofk-dimensional binary linear block codes is constructed with parametersn=2^{k}+2^{k-2}-15,d=2^{k-1}+2^{k-3}-8,k geq 7. Fork geq 8these codes are unique, while there are five nonisomorphic codes fork=7. By shortening these codes in an appropriate way, one finds codes meeting the Griesmer bound for2^{k-1}+2^{k-3}-15 leq d leq 2^{k-1}+2^{k-3}-8; k geq 7.     

Experiments on a semiconductor laser pumped rubidium atomic clock

Experiments were carried out to evaluate the performances of a semiconductor laser pumped rubidium (⁸⁷Rb) atomic clock. Two kinds of Rb gas cells were used and their performances were compared [gas cell A (natural rubidium (⁸⁷Rb/⁸⁵Rb =frac{3}{7}) and buffer gases) and gas cell B (⁸⁷Rb and buffer gases)]. The highest microwave frequency stabilities were estimated as3.4 times 10^{-12} tau^{-1/2}and2.7 times 10^{-12} tau^{-1/2}at the optimal gas cell temperatures of 60°C and 48°C for the gas cellsAandB, respectively (τ: integration time). The light shift, i.e., microwave frequency shift induced by laser light, was measured as -0.50 Hz/MHz and -0.11 Hz/MHz for the gas cellsAandBat their optimal operating conditions given above. As an improved experiment by utilizing high temporal coherence of the laser, a novel double resonance spectral line shape with a drastically narrower linewidth was demonstrated. A technique, similar to FM laser spectroscopy, was employed for this purpose by utilizing laser FM sidebands which are induced by microwave frequency modulation and nonlinear susceptibility of three-level⁸⁷Rb atoms. The minimum linewidth obtained was 20 Hz, which can be used as a sensitive frequency discriminator for an improved⁸⁷Rb atomic clock.     

Characteristics in InGaAs/InP avalanche photodiodes with separated absorption and multiplication regions

Improved characteristics of compound semiconductor avalanche photodiodes with separated absorption and multiplication regions (SAM) are discussed. Temperature dependences of dark current and breakdown voltage show that the tunneling current in the narrow energy gap layer can be suppressed in InGaAs/InP APD's with the SAM structure. Dark currents above punch-through voltages, at which the depletion layer reaches the InP-InGaAs heterointerface, are caused by the generation-recombination process in the InGaAs and at the heterointerface. Dark currents near breakdown depend on the n-layer thickness and are strongly affected by the electric field strength in the ternary layer. Tunneling currents are dominant in diodes with thin n-InP layers, while the generation-recombination processes in the InGaAs layers are dominant in those with a thick n-InP layer. The dark current was as low as7.8 times 10^{4}A/cm²atM = 10when the interface electric field strength is reduced. A maximum multiplication factor of 60 was observed for the6 times 10^{-7}A initial photocurrent. Rise time and full width at half maximum in a pulse response waveform were 100 and 136 ps, respectively, atM = 10.     

Gleason's theorem on self-dual codes

The weight enumerator of a code is the polynomial begin{equation} W(x,y)= sum_{r=0}^n A_r x^{n-r} y^r, end{equation} wherendenotes the block length andA_r, denotes the number of codewords of weightr. LetCbe a self-dual code overGF(q)in which every weight is divisible byc. Then Gleason's theorem states that 1) ifq= 2 andc= 2, the weight enumerator ofCis a sum of products of the polynomialsx^2 + y^2andx^2y^2 (x^2 - y^2 )^2ifq= 2 andc= 4, the weight enumerator is a sum of products ofx^8 + 14x^4 y^4 + y^8andx^4 y^4 (x^4 - y^4)^4; and 3) ifq= 3 andc= 3, the weight enumerator is a sum of products ofx^4 + 8xy^3andy^3(x^3 - y^3)^3. In this paper we give several proofs of Gleason's theorem.     

Analyses of mode-hopping phenomena in an AlGaAs laser

Intensity fluctuations of the longitudinal modes of a 0.8 μm AlGaAs laser were precisely measured during the occurrence of hopping between two modes. It was found from this result that mode hopping follows the stochastics of a Poisson process. The frequency of mode hopping was measured asf_{c} = [exp [-95(I/I_{th} - 1)]] times 10^{7}(Hz). whereI/I_{th}is the injection current normalized to its threshold value. Results of analog computer simulations showed that spontaneous emission worked as a triggering force for mode hopping. Results of the analysis based on the Fokker-Planck equation were compared to the experimental results, from which the root-mean-square value of the fluctuating electric field of spontaneous emission was estimated as2.3 times 10^{2)(V/m)leqlanglesim{E}_{N} leq 3.2 times 10^{2}(V/m). It is concluded that an effective reduction of mode hopping is achieved if the laser is operated at a higher bias or if the coupling constant between the two modes is increased.