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.     

Origin of 1/f noise in bipolar transistors

In planar n-p-n transistors fabricated in IC technology, the dependence of 1/fnoise on the base current density jB, the base width WB, and the emitter area FEwas measured. The power spectrumS_{iB}(f)of the base current fluctuations iBcan be represented by the empirical relationS_{iB} = const. jmin{B}max{gamma} cdot Fmin{E}max{beta} cdot wmin{B}max{-1} cdot f^{-1}where1 leq gamma leq 2and β has been found to be 1.3 or 2. The results of measurements on gate-controlled devices indicate that 1/fnoise cannot be explained by McWhorter's surface model. Therefore, a new model is proposed which assumes resistance fluctuations in the base region as the cause of 1/fnoise in bipolar transistors. The model establishes the relation forS_{iB}(f)as well as the magnitude of the coefficients β and γ.     

Measurement of avalanche multiplication of injected holds in germanium p-n-p diffused-base transistors

A three-terminal dc measurement is made of avalanche multiplication of holes injected from the emitter into the collector junction of diffused-base germanium p-n-p transistors. The method is applicable to asymmetric thin-base transistors at currents at which dc base current is independent of base width when emitter to base voltage (VEB) is held constant. Injected collector current and VEBare measured at constant emitter current as a function of collector to base voltage (V). VEBis measured to take base narrowing into account. Collector reverse current is balanced out. The advantages of this method over two-terminal measurements are that surface, space-charge recombination and internal field emission currents are balanced out and no a priori assumption of the form of the multiplication factorM(V)is needed. For collector barriers which are nearly stepn^{+}pjunctions with the p-type resistivity in the neighborhood of 1 ohm-cm, the multiplication data, which cover the range1.05 siml M siml 2.0, fit the Miller equationM^{-1} = 1 - (V/V_{B})^{n} n = 3.2 pm 0.2in agreement with Miller's two-terminal measurements using alloy and grown-junction Ge transistors. The parameters VBfrom extrapolation of the present data agree within experimental error of five per cent with the collector diode breakdowns BVCBOmeasured by Miller. However, in the present measurements on diffused-base transistors, appreciable surface current multiplication occurs with the result that BVCBOmeasured at 1 ma is approximately 18 per cent less than VB. The absence of microplasma noise in the multiplied injected hole current indicates that multiplication occurs uniformly in the collector barrier under the emitter at least toM = 2.     

Location of 1/f noise sources in BJT's and HBJT's—I. theory

The most general case of1/fnoise in transistors can be described by three independent noise current generators: ibebetween base and emitter, ibcbetween base and collector, and iecbetween emitter and collector. By short-circuiting the base and the collector to ground and comparing the base and collector noise spectraS_{IB}(f)andS_{IC}(f)for the case of zero feedback from the emitter with the base and collector noise spectraS'_{IB}(f)andS'_{IC}(f)for the case of strong feedback from the emitter, one can evaluate the relative strength of the three noise sources. By measuring the current dependence ofS_{IB}(f),S_{IC}(f),S'_{IB}(f), andS'_{IC}(f), one can assign physical processes to the current generators ibc, ibe, and iec. It is the aim of this paper to demonstrate theoretically a simple method for locating1/fnoise sources in BJT's and HBJT's by comparing the base and collector1/fnoise for the cases without and with strong emitter feedback. In later papers we shall demonstrate experimentally how this method is applied to practical situations.     

Low-frequency noise in permeable base transistors

The predominant noise is1/fnoise and consists of two parts: a) Noise varying asImin{C}max{2}, generated mostly with conducting channel and predominating for normal values of the collector voltage VCE. b) Noise at low VCEand practically independent of VCE; it is generated chiefly in the space charge region around the base grating and gives collector1/fnoise atV_{CE} = 0. The turnover frequency of the first noise source lies at about 20 MHz forV_{CE} = 0.30V,V_{BE} = 0.20V. At sufficiently high frequencies the PBT shows thermal noise of the output conductanceg_{c0}at zero bias. Generation-recombination noise is observed at large VBEand low VCEand comes mostly from the space charge region around the base grating.     

Measurement of high-frequency equivalent circuit parameters of junction and surface barrier transistors

Methods are described for the determination of the high-frequency parameters of junction and surface barrier transistors and involve, in addition to the knowledge of the usual low-frequency parameters, measurement of the product of Ccand the extrinsic base resistancer_{b0},r_{b0}itself, and the alpha cutoff frequency fα. A previously described method is used to determine the productr_{b0}C_{c}, but new methods are described for the measurement ofr_{b0}and fα. The measurements are of "bridge" type, involving simple circuit adjustments for a response null at a single frequency. Typical experimental results are given for transistors having fαvalues as high as 85 mc, Ccvalues down to 2.3 pF andr_{b0}ranging from 45 to 400 ohms. The limits quoted for fαand Ccrefer to surface barrier transistors. Comparison with results derived by alternative methods of measurement show good agreement.     

Direct measurement of the potential spike energy in AlGaAs/GaAs single-heterojunction bipolar transistors

A balanced two-step current transport theory, i.e., thermionic emission followed by Shockley diffusion, is applied to study the emitter-base (EB) potential spike energy in the AlGaAs/GaAs single-heterojunction bipolar transistor. It is found, surprisingly, that when the transistor is operated in the active region theI-Vcharacteristics of the collector current (IC) versus base-emitter applied voltage (VBE) exhibits an ideality factor of 1.237. This non-1kT transfer characteristics is due to the bias-dependent potential spike energy at the emitter-base heterojunction. The reverse I-V characteristics of emitter current (IE) versus base-collector bias (VBC), however, shows the traditional 1kT behavior. The difference between ICand IEat the same applied voltage (V_{BE} = V_{BC}) determines the potential spike energy (ΔE). It turns out that Δ E/q = 0.19(V_{BE} - 0.48)whereqis the unit charge. This indicates that the potential spike appears only when the applied voltageV_{BE} > 0.48V.     

The effect of collector capacity on the transient response of junction transistors

The effect of collector depletion layer capacity on the transient response of junction transistors to a current input is calculated for the case of a resistive load. Expressions are given for the small-signal rise-time of the common-base, emitter, and collector configurations and for the large-signal turn-on and decay times of the common-emitter and collector configurations. The analysis shows that the transient durations under most conditions of operation are approximately (1 + omega_{alpha}R_{L}C_{c}) times those which would be predicted for the short-circuit output approximation reported by Moll [1]. Experimental results are reported which exhibit an excellent agreement with the analysis over a wide range ofomega_{alpha}R_{L}C_{c}. An empirical examination has been made of the dependence of large-signal switching time on the range of operating point excursion. A satisfactory approximate representation of this dependence is provided by a first-order correction factor, which takes into account the functional dependence of ωαand Ccon collector voltage.     

Noise figure of UHF transistors as a function of frequency and bias conditions

It is shown that the observed values of the minimum noise figureF_{min}of UHF transistors in common base connection can be explained in terms of the device parameter(1-alpha_{dc}) r_{b'b}/R_{e0}and fαfor frequencies up to 1000 MHz. An interesting collector saturation effect is observed that gives a strong increase in UHF noise figure at high currents. Many features of the dependance ofF_{min}on operating conditions can be explained by this effect. The current dependence ofF_{min}for large values of |VCB| and high currents suggests a distribution in diffusion times through the base region. At intermediate frequencies, the noise figure increases with increasing collector bias |VCB| due to an increase inr_{b'b}, which in turn is caused by the dependence of the base width on |VCB|.     

Threshold voltage scattering of GaAs MESFET's fabricated on LEC-grown semi-insulating substrates

Threshold voltage standard deviation (sigma V_{th}) for MESFET's on a liquid encapsulated Czochralski (LEC) grown GaAs wafer was investigated, in connection with dislocation distribution. Threshold voltage (Vth) scattering was found to be strongly correlated to the dislocation cell network structure in the substrate. This dislocation cell network is characteristic of the LEC-grown crystal. At largesigma V_{th}region, strongly networked dislocation cell structure was observed. In the area where dislocations distributed randomly without network structure,sigma V_{th}was small in spite of high dislocation density. For FET's located in the dislocation-free region inside the network cell, low drain current Idsand high Vthwere recognized directly by a curve tracer. The experimental results regarding the dislocation network effect on Vthscattering are discussed along with cathodoluminescence study results.     

Optimum Radar Signal-Filter Pairs in a Cluttered Environment

In a recent paper on radar detection in clutter, the authors stated that the signal-to-interference ratiorho_{cf} (u)obtained with the signaluand its optimum filter can have stationary points which are not stationary points ofrho_{mf} (u), the signal-to-interference ratio obtained withuand its matched filter, even when the clutter distribution in range and Doppler is symmetric. This letter strengthens this statement and exhibits an example to support it. The stronger statement is the following: Even for symmetric clutter distributions, the global maximum ofrho_{cf}can exceed the global maximum ofrho_{mf}.     

Efficient V-V energy transfer in a multiphoton excited mixture of SF6and CF4

Spectral and temporal measurements of infrared fluorescence (IRF) in SF6, CF4, and mixtures of SF6and CF4gases excited by a pulsed CO2laser are reported. Using the 944.2 cm^-1[P(20)] laser line for excitation and measuring the IRF spectra between 700 and 1500 cm^-1, a strong red shifted IRF peak of the ν3mode in pure SF6was found. No IRF was observed under these conditions in pure CF4. In a 13:10 mixture of SF6and CF4, two strong IRF peaks of the ν3modes, shifted to the red relative to the room-temperature fundamentals at 948 cm^-1and 1283.2 cm^-1, were observed. The peaks are almost equal in height and since both molecules have almost the same ν3band intensity, the present result suggests that efficient intermolecularV-Venergy transfer occurs from excited SF6to cold CF4molecules. The temporal behavior of the IRF signals under high excitation (langlenrangle approx 6) in pure SF6exhibits two relaxation times, one of bulk cooling withtau_{1} approx 1ms and the other of aV-Tnature withPtau_{2} approx 20 mus . torr. In the mixture, an additional relaxation of the intermolecularV-Venergy transfer process is observed withPtau_{3} approx 10 mus . torr. The red shift dependence of the IRF peaks on the degree of excitation was also measured and used to examine population distributions, specific IRF transitions, and anharmonicity parameters.     

The effect of distributed series resistance on the dark and illuminated current—Voltage characteristics of solar cells

Distributed series resistance effects in solar cells are analyzed and the correctness of representing these by a lumped parameter is discussed for any conditions of bias and illumination. In addition to a general mathematical methodology, analytical expressions are derived to simplify the estimation of series resistance effects on the dark and illuminatedJ-Vcharacteristics of the cell. The equivalent series resistance (rs) in the dark is found to decrease with current densityJfromr_{b} + r_{e}/3at smallJto (r_{e} r_{b})^{1/2}at very highJ, where reand rbare the emitter layer and base region resistances, respectively. For illuminated conditions rsdepends onJas well, being maximum near short-circuit and minimum near open-circuit; however, rsfurther depends on the photogenerated current JL: its short-circuit value increases with JLfromr_{b} + r_{e}/3tor_{b} + r_{e}/2and the open-circuit value decreases with JLfromr_{b} + r_{e}/3to(r_{e}r_{b})^{1/2}. The variability of rsis therefore related to the relative importance of rbandr_{e};r_{b}plays the role of attenuating this variability, a situation not well recognized previously. Previous theoretical and experimental work is critically reviewed throughout this paper.     

Noise temperature in silicon in the hot electron region

The noise temperature as a function of the applied field has been measured on an epitaxial silicon layer at the frequencies 2 GHz and 4 GHz. It has been found that the experimental results are in good agreement with the theory given by Moll. It is shown that for noise calculations in silicon field-effect transistors with pronounced carrier velocity saturation the noise temperature Tnversus field E may be approximated byT_{n}/T_{0}= 1 + γ(E/E_{c})^{2}with T0= lattice temperature, Ec= saturation field, γ = const.     

Epitaxial π-ν n-p-n high-voltage power transistors

A new silicon power-transistor structure has been developed which expands the frontiers of power-switching performance and high-voltage power-handling capability. This new structure employs a unique π-ν (nearly intrinsic p- and n-type) epitaxial-layer construction which utilizes "overlay" emitter concepts to achieve improved volt-ampere densities and expanded second-breakdown performance. An n⁺-p-π-ν-n⁺transistor structure is constructed using alternately grown π and ν, epitaxial high-resistivity layers, p-type base and n⁺emitter diffusions are used in the conventional manner to assure punch-through protection. The depletion region for the n⁺-p-π-ν-n⁺transistor is in the π base and the ν collector, and the maximum electrical field (E_{max}) is at the π-ν interface. The avalanche breakdown VBof the device can be controlled by the thickness (X_{n}, X_{p}) and the concentration (N_{A}, N_{D}) of the π-ν layers. Limiting the thickness of the ν collector region and adjusting the thickness of the π base layer provides a transistor with optimum volt-ampere capability. Various π-ν structures have been fabricated and are evaluated electrically for power switching and for linear applications.     

The temperature dependence of the DC base and collector currents in silicon bipolar transistors

Detailed measurements have been made of the base and collector-current characteristics of both n-p-n and p-n-p silicon transistors as a function of temperature. The collector current shows ideal behavior over the temperature range -60 to 150°C in thatI_{C} infin exp (eV_{BE}/kT). On the other hand, the base current is nonideal:I_{B} infin exp (eV_{BE}/nkT), wheren > 1.0. The nonideality of IBis the main source of the temperature dependence ofh_{FE} = I_{C}/I_{B}. There is no evidence for bandgap narrowing in the devices we have investigated. The temperature dependence of the collector current is given byI_{C} infin T_{m} exp (-e E_{g0}/kT) exp (eV_{BE}/kT), wherem = 1.4or 1.7 for n-p-n or p-n-p devices, respectively.E_{g0} = 1.19 pm 0.01eV. This result is consistent with the findings of others. The base current is a complicated function of temperature due to the presence of nonideal components.     

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.     

The area of safe operation of transistors for switching operation

A thermal feedback model is presented for the analytical definition of the ASO (Area of Safe Operation) for transistors in switching operations. This area is narrowed by the "second breakdown in p-n junction," and the approximate representation of the breakdown threshold is presented. This model consists of a forward and feedback energy flow with gains A and B, respectively.A = V_{CE} times M, B = K times theta times alpha_{R} times I_{e}. Therefore, the condition of the breakdown can be introduced as1 - AB = 0, whereMis the current multiplication factor, θ is transient thermal resistance,Kis a newly introduced current concentration factor, and αRis the temperature coefficient of Ie. Experimental results are also reported for a germanium alloy type transistor.     

A laser augmented reaction: SF6+ SiH4→S*2+ SiF4+ HF + H2· retention of isotopic selectivity during detonation

A single unfocused pulse of a free running CO2laser, area ∼ 8 cm², initiates an explosive reaction between SF6and SiH4. This occurs at a minimum energy of 4 J [full width at half maximum (FWHM)sim 1.5 /mus] of which about one half is absorbed in an 8 cm long cell; total pressure 12 torr; 0.65 <p(SiH4)/p(SF6) < 1.8. The spectral and temporal distributions of the emitted chemiluminescence depend sensitively on the fuel to oxidizer ratio, and on the pulse energy; we investigated the range 4 → 20 J. The principal emission is due to S2(B^{3}Sigma-_{u} rightarrow X^{3}Sigma-_{g}). Transitionsupsilon' (0-4) rightarrow upsilon" (2-15)were recorded. In the³Sigma-_{u}state, vibrational temperatures range from 3000-13000 K. The luminosity peaks sharply at (SiH4)/(SF6) = 1.0 ± 0.05. On each side of the maximum of the emission versus composition curve [at (SiH4)/(SF6) ≈ 0.95 and 1.22, for a 12 J pulse] the residual SF6(0.2-0.5 percent of initial amount) is enriched in³⁴SF6; the observed fractionation factors at these two compositions are 8 ± 2. The separation between the two sharply peaked optimum compositions appears to increase with increasing pulse energy. Preliminary results with other fuels suggest that the concurrent absorption of CO2laser radiation by the fuel, as well as a highly exothermic reaction, are pre-requisite for fine tuning of composition, injected power, and total pressure for optimum isotope fractionation.     

Ultralinear UHF power transistors for CATV applications

An investigation of the cross-modulation performance of UHF power transistors and its correlation with the gain parameter curves S21(IC, VCB) shows that such transistors today exhibit an inherent linearity limitation and are not optimized for ultralinear applications. This means that using higher power transistors does not result in a larger output signal with low cross-modulation distortion. Presented measurements clearly demonstrate that the nonlinear products increase, not only with increasing emitter dc current, but also with collector voltage above certain limiting values ICLand VCL, respectively; ICLand VCLare relatively small compared with the corresponding maximum permissible values of ICand VCB. Their existence can be explained by current crowding effects, by the space-charge limitation of the collector current, by the nonuniform thermal conductance, by the temperature gradients, and by the unequal current density distribution across the (large) active areas of power transistors. A correlation between the VCgain parameter falloff effect and the "thermal distortions," has been established. Design and selection criteria for ultralinear transistors needed in CATV amplifers are given. A simple linearity test method is described.