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.     

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.     

The influence of post-emitter processing on the current gain of bipolar transistors

The effects of post-emitter processing on the current gain of n-p-n and p-n-p transistors used in linear integrated circuits, is the subject of this paper. It is seen that during the emitter diffusion deep level impurities segregate into the bulk and space-charge regions of the emitter. The aluminum alloy process at 500°C provides a powerful scavenging action that getters the impurities. The post-alloy current gain increases by a factor of ten. This gettering is effective in phosphorus diffused emitters if the dielectric is either a CVD oxide, a plasma deposited oxide, or phosphorus glass under Si3N4. With thermally oxidized emitters there is no improvement in current gain. Boron diffused emitters, however, respond to the aluminum alloy process regardless of the dielectric. This study also identifies two processes that contribute to bandgap narrowing (DeltaE_{g}) these are the emitter diffusion and the post-emitter thermal oxidation. A value ofDeltaE_{g}= 0.04 eV measured after the emitter diffusion was found to increase to 0.09 eV after thermal oxidation at 975°C. This additional component ofDeltaE_{g}is a result of the anomalous accumulation of phosphorus at the silicon surface during oxidation.     

Second breakdown of double epitaxial transistors

This paper deals with the second breakdown of transistors with epitaxial collector, epitaxial base, and diffused emitter. Transistors were fabricated with base width WBin the range of 2 to 18 µ and resistivity in the range of 0.1 to 10 ohm . cm. The optimum values of the resistivity and the thickness of these regions were calculated by computer techniques. The devices were mounted onto a TO-63 header and the base and the emitter leads were bonded onto the device ultrasonically. The electrical characteristics, including the frequency response ftand secondary breakdownS/Bcapability, were tested. For the measurement of second breakdown current IM, forward bias condition was used. It was found that for fixed collector and emitter parameters, IMwas controlled by the product of base resistivity ρBand base width WB. The value of IMwas found to increase withrho_{B}W_{B}. However, for a specified device characteristic, an optimum value ofrho_{B}W_{B}was found to exist. For transistors withV_{CEO} =150volts,f_{t}=20mHz andh_{FE}=20, the optimum value ofrho_{B}W_{B}was found to be 6 × 10^-4ohm . cm².     

Photosolubility of diazoquinone resists

The photochemical properties of a diazoquinone/novolak resist system were studied over a wide range of material and processing parameters in order to determine the optimum values for a given application. These resists are representative of the commercial positive-working photoresists being used for high-resolution lithography. The solubility of the resist in an alkaline developer depends on exposure E asDelta g^{-1} = [g_{0}(E/E_{e})^{m}]^{-1} + [Delta g_{infin}]^{-1}where the net development rate (Delta g) is the difference between solubility rates of the exposed (g) and unexposed (g0) sample. Three of these parameters characterize the lithographic response of the resist. They depend mainly on the resist composition but not on the processing conditions. Eeis a measure of the sensitivity and ranges from 10 to 20 mJ/cm²of 405-nm light for useful resist formulations. The contrast parameter (m) increases slowly with sensitizer concentration while the saturated solubility ratio (g_{infin}/g_{0}) inereases very rapidly. The fourth parameter (g0) depends strongly on processing parameters. It can readily be set to provide the desired development time, e.g., by adjusting the developer strength. On a more fundamental level, it is found that the dependence of the solubility on exposure can be expressed in a unified manner for all the resist formulations studied asg approx g_{0} exp (2 times 10^{-20} n_{e})where neis the number of exposed sensitizer molecules per cubic centimeter.     

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.     

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.     

InGaAs/InP double-heterostructure bipolar transistors with near-ideal β versus ICcharacteristic

InGaAs/InP double-heterostructure bipolar transistors (DHBT's) with current gain β ∼ 630 have been realized using gas-source molecular beam epitaxy (GSMBE). These devices exhibit near-ideal β versus ICcharacteristic (i.e., β independent of IC) with a small-signal gainh_{fe} sim 180atI_{C} sim 2nA. In comparison, we findbeta sim I_{C}^{0.5}for a high-quality AlGaAs/GaAs HBT grown by OMCVD. The higher emitter injection efficiency at low collector current levels found in the InGaAs/InP DHBT is due to at least a factor 100 smaller surface recombination current.     

The saturated photovoltage of a p-n junction

Assuming the conventional divisions of the semiconductor into depleted and neutral regions, it is shown that for an abrupt p-n junction with nondegenerate carriers a relation exists between the open circuit photovoltage and the PN product at the junction(PN)_{0}, which is valid for all signal levels. In the small-signal case this leads to the standard result. At intermediate levels a new relationV = KT/q (1 pm m) log_{e} ([(PN)_{0}]^{1/2}/n_{i})holds, the upper sign for p+-n junctions, the lower for n+-p junctions;m = (micro_{e}-micro_{h})/(micro_{e}+micro_{h}). At very high levels the photovoltage saturates toV = kT/q[log_{e}(M_{p}M_{n}/n_{i^{2}}) + m log_{e}(micro_{h}M_{p}/micro_{e}M_{N})]. Since Mpand MNare the doping levels in the p and n regions, the first term is the diffusion potential and the second term will be positive for p+-n junctions and negative for n+-p junctions. These results compare satisfactorily with the available experimental data.     

Computer-aided design consideration on low-loss p-i-n diodes

Two methods are presented to realize a low forward-voltage p-i-n diode with a thin i region. One is to increase recombination current by appropriately controlling carrier lifetime in the i region. The recombination current for a constant voltage reaches a maximum at a carrier lifetime given by(q/kT) Wmin{i}max{2}/8mu_{i}, where Wiand μiare thickness and effective mobility of the i region, respectively. The other is to increase diffusion current in the p emitter by decreasing carrier lifetime only for the high impurity concentration region. On the basis of the first method, diodes with a 0.83-V forward voltage at 150 A/cm², a 200-V reverse voltage, and a 50-ns reverse recovery time were obtained.     

Geometrical factors in avalanche punchthrough erase

It is known that the surface potential of an IGFET can be raised to high levels by reverse-bias pulsing its source and drain. This high surface potential is contingent upon both punchthrough and avalanche injection of majority carriers into the surface region. Erase of some multilayer charge storage memory cells is accomplished using such an avalanche punchthrough erase (APTE) operation. In this paper the maximum surface potential achievable in this manner is assessed for a variety of geometries. The calculation is based upon a Fourier sine transform solution of Poisson's equation, coupled with the sampling theorem for spatially localized functions. The depletion width is determined self-consistently and is found to vary from a minimum value at mid-channel to a maximum value at the channel ends. It is found that the maximum surface potential is achieved for devices whose junction depth is comparable to or greater than the channel length. Under these conditions the surface potential can be as large as the reverse bias less the punchthrough voltage. To avoid serious short-channel behavior during normal read operations, it is suggested that the conditionNl^{2} > 2V_{D}kisin_{0}/ebe observed, whereN= doping level/cm³,l= half channel length, VD= drain voltage during read, K = dielectric constant of semiconductor, ∈0= permittivity of free space,e= electronic charge. Thus for a 2-µm channel length we recommend a junction depth ≥2 µm, and a doping level ≈6.5 × 10¹⁵/cm³for a memory cell which is to use APTE and a read voltageV_{D} simeq 5V.     

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.     

Experimental and theoretical studies of third-harmonic generation in the chalcopyrite CdGeAs2

Experimental and theoretical studies of third-harmonic generation (THG) in the chalcopyrite semiconductor CdGeAs2are presented. The phase-matching configurations for THG are analyzed from the irreducible components point of view. A theory of the bound electron and free-carrier contribution to the third-order susceptibility is presented. The experimental results are given. The effective nonlinear coefficient for type-II THG is mainly due to the free-carrier contribution, and for a hole concentration of5 times 10^{16}/cm³it is measured to be(13 pm 6)10^{-11}ESU. The practical applications of THG in CdGeAs2are discussed.     

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.     

Flexible Full-Color AMOLED on Ultrathin Metal Foil

Full-color active-matrix organic light-emitting diode panels, driven by poly-Si thin-film transistors (poly-Si TFTs), were successfully fabricated on thin metal foil substrates. The p-channel poly-Si TFTs on metal foil showed a field-effect mobility of 82.9 $hbox{cm}^{2}/hbox{V}cdothbox{s}$ , subthreshold slope of 0.34 V/dec, threshold voltage of $-$ 1.67 V, and off-current of $ hbox{6.6} times hbox{10}^{-14} hbox{A}/muhbox{m}$. The 5.6-in panel had 160 $times$ RGB $times$ 350 pixels, each of which had a pixel circuit of two TFTs and one capacitor.      

Heavily doped transparent-emitter regions in junction solar cells, diodes, and transistors

An analytical treatment of heavily doped transparentemitter devices is presented that includes the effects of bandgap narrowing, Fermi-Dirac statistics, a doping concentration gradient, and a finite surface recombination velocity S at the emitter surface. Transparency of the emitter to minority carrier is defined by the condition that the transit time τtis much smaller than the minority carrier lifetime in the emitter τp,tau_{t} ll tau_{p}. As part of the analytical treatment, a self-consistency test is formulated that checks the validity of the assumption of emitter transparency for any given device. The transparent-emitter model is applied to calculate the dependence of the open-circuit voltage VOCof n⁺-p junction silicon solar cells made on low-resistivity substrates. The calculated VOCagrees with experimental values for highS_{P}( geq5 \× 10^{4}cm/s) provided the effects of bandgap narrowing (modified by Fermi-Dirac statistics) are included in the transparent-emitter model.     

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.     

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.     

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).     

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|.