Performance of InxGa1-xAsyP1-yphotodiodes with dark current limited by diffusion, generation recombination, and tunneling

We present a theoretical study of the effects of diffusion, generation-recombination (GR), and the recently observed tunneling currents on the performance of photodiodes made from In0.73Ga0.27As0.63P0.37and In0.53Ga0.47As. Calculations are made for both p+ν and p-i-n punch-through diode configurations, and are compared with recent measurements made by several independent investigators. For doping densities typical of present material (N_{D} gsim 10^{15}cm^-3), tunneling currents become dominant prior to avalanche breakdown. Thus, for detection of weak (-55 dBm at 45 Mbits/s) optical signals, the diodes must be operated at low voltages where GR is the dominant source of reverse-biased leakage. To meet the requirements of low capacitance (C leq 0.5pF for a diode area of 10^-4cm²) and low GR dominated dark current (I_{D} leq 10nA atT = 70degC), the doping density and effective carrier lifetime (τeff) must beN_{D} < 7 times 10^{15}cm^-3andtau_{eff} gsim 150ns for In0.73Ga0.27As0.63P0.37and5 times 10^{14} lsim N_{D} lsim 7 times 10^{15}cm^-3andtau_{eff} gsim 3.5 mus for In0.53Ga0.47As.     

Electronic processes at grain boundaries in polycrystalline semiconductors under optical illumination

The dependence of minority carrier lifetime (τ) on the doping concentration Nd, grain sizedand interface state density Nisat the grain boundaries in (n-type) polycrystalline semiconductors has been calculated analytically. The recombination velocity at grain boundaries is enhanced by the diffusion potential Vdadjacent to the boundaries, and ranges fromsimeq 10^{2}to 10⁶cm . s^-1depending on Nisand Nd. Under illumination, the population of the interface states is altered considerably from its dark level and as a result, Vddecreases to that value which maximizes recombination (equal concentrations of electrons and holes at the boundary). This causes τ to decrease with increasing Nd. Sample calculations for polycrystalline silicon show that for low angle boundaries with interface state densities ofsimeq 10^{11}cm^-2eV^-1, τ decreases from 10^-6to 10^-10s as the grain size is reduced from 1000 to 0.1 µm (forN_{d} = 10^{16}cm^-3). For a constant grain size, τ decreases with increasing Nd. The open-circuit voltage of p-n junction solar cells decreases fortau leq 10^{-7}s, whereas that for Schottky barrier cells remains at its maximum value untiltau lsim 10^{-8}s.     

Linear microwave amplification with Gunn oscillators

Linear microwave amplifiers with continuous power outputs of 100 mW have been constructed utilizing the frequency-independent negative conductance observed externally in Gunn oscillators. This negative conductance is exhibited only in samples containing propagating dipole layers, in other words,n_{0} . Lmust be larger than 10¹²cm^-2for n-GaAs. The output power obtainable from this amplifier is substantially larger than that from a subcritically doped GaAs amplifier (n_{0} . L < 10^{12}cm^-2) becausen_{0} . Lcan be increased. Power output and efficiency are discussed in terms of n0andL. The upper-frequency limit for amplification is determined by the time the domain takes to readjust itself after a change of external voltage which leads to an upper limit for thef. Lproduct (about 10⁸cm/s). The essential feature of the amplifier circuit is to provide both a short circuit at the Gunn oscillation frequency and a broadband circuit at the signal frequency. An average gain of 3 dB was exhibited from 5.5 GHz to 6.5 GHz. Gain compression of 1 dB occurred at 60 mW output power with 9 dB gain, while the noise figure was about 19 dB.     

Thermionic current in a parallel-plane diode

An approximate formula is developed for the current of a parallel-plane diode including the effects of initial velocities of emission. For an oxide-coated cathode (T = 1000°K) the approximate result is:J = 2.33 times 10^{-6} frac{V^{3/2}}{x^{2}} cdot[1 + frac{11.4(J_{s}x^{2})^{1/4}}{V^{3/4}} + frac{3.22(J_{s}x^{2})^{1/8}}{V^{3/2}}]where,J, Js, andxare in suitable units such that Jx²andJ_{s}x^{2}are in amperes and V in volts. A comparison is made between this result, Child's 3/2 power solution, and the Epstein-Fry-Langmuir solution. The result given above being an explicit solution of the current is particularly advantageous over prior approximate solutions.     

On the dark currents in germanium Schottky-barrier photodetectors

It is shown that for experimentally observed values of Schottky-barrier height of metal-n-type germanium photodetector structures, the dominant component of dark current can be due to the injection of minority carriers, rather than to the usual majority-carrier component. For barrier heights approaching 0.6 eV, for doping concentrationsN_{d} lsim 10^{15}cm^-3, for short minority-carrier lifetimetau_{p} lsim 1µs, for narrow base widthW_{b} lsim 10µm, or combinations of these conditions, the minority-carrier injection ratio approaches unity and these devices behave in the same way as p⁺-n junctions, with identical dark currents. The low-temperature fabrication requirements and processing simplicity of germanium Schottky barriers makes these devices more attractive under these conditions than germanium p-n junction photodetectors.     

A treatment of diffusion errors affecting junction depth

An error treatment of the diffusion variables of time t, temperature T, and starting resistivity ρ, has been made in regard to their effects upon junction depth. An analytical equation has been derived for engineering usage in determining the per cent error in junction depthx: Per cent error in junction depth =100 sqrt{frac{bar{Δt^{2}}{2t}} +frac{bar{QΔT}^{2}}{2RT^{2}}+bar{frac{sqrt{pi DT}}{microq p^{2}N_{s}x}. Delta rho exp (x^{2}/4Dt)}}A sample calculation using the above equation is presented along with a method of estimating errors in junction depth due to heating and cooling in the diffusion cycle.     

A fast, high-current pulsed discharge device for the inner-shell excitation of atoms and ions

We report the operation of a fast-pulsed, high-current, table-top discharge device for the excitation of large densities of energetic atomic and ionic levels. The peak current through the discharge was measured to be 16.4 kA at a current density of approximately 1.1 kA . cm^-2. A high degree of excitation of energetic states of atomic and ionic Cs by "hot" electrons in the negative glow discharge was demonstrated by population measurements and VUV emission studies. In particular, the population density in the level Cs II (5p^{5}6s) 3/2[3/2] J = 2, at 13.33 eV above the Cs II ground state, was measured to be(6 pm 4) times 10^{12}cm^-3at a measured electron density of(1.3 pm 0.5) times 10^{14}cm^-3. The population densities of energetic atomic and ionic levels examined in this work were an order of magnitude larger than those produced in previous discharge devices.     

Stability criterion for Gunn diodes with injection-limiting cathodes

According to McCumber [1] a Gunn diode with an ohmic cathode (i.e., "differential cathode conductivity"sigma_{c} = delta) is stable in a constant-voltage circuit ifn_{0}L le (n_{0}L)_{crit} equiv 2.7 times 10^{11}cm^-2wheren_{0}Lis the doping-length product. We show that the same stability criterion applies to Gunn diodes with an injection-limiting cathode(sigma_{c} rightarrow 0), if(n_{0}L)_{crit}is allowed to be a function ofsigma_{c}L. The value of(n_{0}L)_{crit}increases by 30 percent if(sigma_{c}L)varies from infinity (ohmic cathode) to zero (injection-limiting cathode). If a cathode with negative differential conductivity is realizable, it may be possible to extend the(n_{0}L)region of stable operation of Gunn diodes drastically.     

Optical absorption and fluorescence studies in high pressure cesium-xenon mixtures

The pressure and temperature dependent absorption and fluorescence spectra of the cesium-xenon (CsXe) molecule have been examined. In contrast to previous investigations of the alkali-rare gas molecules, cesium atomic states that have weakly allowed optical transitions have been studied and have been shown to form excimer levels that are attractive for application as potential dissociation lasers. In particular, the (Cs[7^{2}S]Xe)* excimer appears promising as a source of high-energy laser radiation due to 1) its large dissociation energy (0.132 eV), 2) its stimulated emission cross section ofsimeq10^{-17}cm², and 3) its small population threshold inversion densities (simeq10^{13}cm^-3).     

Modes in lossy stratified media with application to underground propagation of radio waves

The problem considered is that of determining the complex propagation constant of a plane wave on a flat layer of lossy dielectric with a loss-tangent of less than one, and of uniform thickness, surrounded on both sides by identical layers having a loss-tangent greater than one, and thicknesses much larger than the skin depth. A formula given, relates this propagation constant to the path loss between two antennas provided their excitation efficiencies are known. As an example, curves showing attenuation and wavelength are given for the following properties of the layers: Middle layer =sigma = 10^{-6}(ohm meter)^{-1},epsilon_{r} = 10, mu_{r} = 1. Surrounding layers =simga = 10^{-2}(ohm meter)^{-1},epsilon_{r} = 10,mu_{r} = 1. Frequencies between 1 kc and 10 Mc are covered, as well as values on thickness of the meddle layers ranging from 10 m-200 m. (The computations were performed under the direction of John Nihen).     

Channel waveguides in glass via silver-sodium field-assisted ion exchange

Multimode channel waveguides were formed by field-assisted diffusion of Ag+ ion from vacuum-evaporated Ag films, into a sodium aluminosilicate glass reported to yield high diffusion rates for alkali ions. Two-dimensional index profiles of channel waveguides formed by diffusion from a strip aperture were controlled by means of diffusion time, temperature, and electric field. The diffusion equation for diffusion through a strip aperture in the presence of a one-dimensional electric field was solved. Its solution was in agreement with measured concentration profiles:frac{C(x,y,t)}{C_{0}} = frac{1}{2} { erf (frac{a - x}{2sqrt{Dt}}) + erf (frac{a + x}{2sqrt{Dt}})}.frac{1}{2} { erfc (frac{y - muE_{y}t}{2sqrt{Dt}}) + e^{(yE_{y}/D)} erfc (frac{y + muE_{y}t}{2sqrt{Dt}})}Diffusion coefficients in this aluminosilicate glass were determined to beD =(2.41 times 10^{-13}) (frac{m^{2}}{s})).exp (frac{-3.1 times 10^{4}frac{J}{mol}}{RT})Diffusion coefficients were higher (between 150°C and 300°C) than those of a low-iron soda-lime silicate glass "standard" also studied, for which diffusion coefficients wereD =(3.28 times 10^{-13} (frac{m^{2}}{s})).exp (frac{-3.6 times 10^{4}}{RT} (frac{J}{mol}))This difference in diffusion coefficients is due to the higher activation energy of diffusion in the soda-lime silicate glass. The Gladstone-Dale relation was used to calculate the maximum possible refractive index change via Ag+-Na+ ion-exchange for each type of glass. The maximum index change in the sodium aluminosilicate glass is found to be about 65 percent of that in the soda-lime silicate glass.     

Two types of microwave emission from InSb

Two types of microwave emission from InSb plasma subjected to the crossed electric and magnetic fields were investigated experimentally. From the simultaneous measurements of Hall effect and microwave emission, the threshold condition of the one type of emission was obtained as(omega_{ce} tau_{e})^{2} cdot Delta n geq 3 times 10^{14}cm^-3, whereomega_{ce}, tau_{e}, andDelta nare electron cyclotron frequency, relaxation time, and electron-hole pair density, respectively. It was also found that the "Hall" mobility showed anomalous decrease above the threshold. The emission power of the other type of emission showed maximum value at several values of the applied magnetic field lower than the threshold of the noise-type emission. These characteristic magnetic fields were not influenced by current density except by slight change in the low-current density region.     

Impact ionization in bulk GaAs high field domain

An investigation of impact ionization in the high field domains of GaAs Gunn effect devices has been carried out. A method of measuring the number of excess electrons generated per domain transit was developed, based on the measurement of the increase in the valley current from one domain transit to the next while impact ionization is occurring in the domain. This method was used to experimentally determine the carrier generation per domain transitDelta n/n_{0}as a function of excess domain potential VDfor three material carrier concentrations. These results are compared to a theoretical calculation ofDelta n/n_{0}based upon an approximate solution of the continuity equation and invariant domain calculations. The experimental and theoretical results agree to within 2 percent forn_{0} = 3 times 10^{14}cm^-3and 6 percent forn_{0} = 4 times 10^{14}cm^-3.     

Temperature dependence of MOSFET characteristics in weak inversion

A knowledge of the MOSFET operating in weak inversion is important for circuits with low leakage specifications. This paper discusses the effect of temperature on the MOSFET in weak inversion. The reciprocal slopenof the log IDSversus VGSrelationship between source-drain current IDSand gate bias VGSmay be given byfrac{1}{(n - 1 - gamma)^{2}} = frac{2Cmin{ox}max{2}}{qepsilon_{s}N_{B}} [frac{3}{4} frac{E_{g^{0}}{q} - (frac{3}{2}alpha + frac{k}{q})T]withalpha equiv (k/q)(38.2 - ln N_{B} + (3/2) ln T)and γ ≡C_{ss}/C_{ox}, where Coxis the oxide capacitance per unit area, Cssthe surface states capacitance per unit area,qthe electronic charge, εsthe permittivity of silicon, NBthe bulk doping concentration,kthe Boltzmann's constant,Tthe absolute temperature, andE_{g0}the extrapolated value of the energy gap of lightly doped silicon atT = 0K. This theoretical formula was in good agreement with experimental results in a temperature range of interest.     

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).     

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}     

Performance of In0.53Ga0.47As/InP avalanche photodiodes

We calculate operating characteristics of high-sensitivity high-speed In0.53Ga0.47As/InP avalanche photodiodes (APD's). We find that significant photocurrent gain is obtained for a total fixed-charge density ofsigma_{tot} > 3 times 10^{12}cm^-2in the depleted InP and0.53Ga0.47As regions. To obtain high quantum efficiency and low tunneling currents, the fixed-charge density in the InP must be in the range2 times 10^{12}cm^-2leq sigma_{B} leq 3 times 10^{12}cm^-2. We calculate the breakdown voltages for APD's with uniformly doped layers and find that practical detectors with avalanche breakdowns as low as 15 V can be realized. High quantum efficiency and fast response are obtained by compositional grading of the In0.53Ga0.47As heterointerface over a distance ofL gsim 380Å, depending on the doping and amount of the In0.53Ga0.47As layer swept out at breakdown. Finally, a comparison of calculations with experimental results is presented.     

Influence of ΦMS(T) in the determination of the Si-SiO2surface states

The determination of fast surface states at the Si-Si02system by the Gray-Brown low-temperature technique is carefully analyzed. Included in this analysis is the variation of the semiconductor work function with the temperature and the doping impurity partial ionization at low temperature. It is shown that particularly the influence of the semiconductor work function is very significant. For instance, we obtained for an Si-SiO2system a number of surface states, with energy levels between 0.32 and 0.53 eV,N_{fs} simeq 8.5 times 10^{9}cm^-2orN_{fs} simeq 1.0 times 10^{11}cm^-2, the difference due to the influence of the semiconductor work function only.     

Radiative efficiencies of radio frequency sulfur discharges

The radiative efficiencies of RF sulfur discharges under various conditions of power loading, sulfur vapor pressure, and argon buffer pressure have been determined. The highest CW efficiency was 11 percent for a sulfur density of6.3 times 10^{16}cm^-3and 20 torr argon buffer. The results of pulsed operation show that the efficiency increases slightly to 13 percent for a sulfur density of8.8 times 10^{16}cm^-3.     

A simplified capless annealing of GaAs for MESFET applications

A simple capless annealing technique for post-implantation annealing of a GaAs wafer is described. The technique incorporates a novel boat design and uses InAs as the source of arsenic overpressure. Using this technique, wafers annealed at 850°C show mobilities in the range of 4000 cm². V^-1. S^-1with over 85-percent activation for a Si dose of5 times 10^{12}cm^-2. Dopant depth profiles with peak donor densities of2 times 10^{17}cm^-3and minimal tailing were demonstrated. Electron channeling data show that crystallinity is fully restored during the anneal. 1-µm gate length MESFET's processed on n⁺-n implanted layers exhibitedg_{m} geq 160mS/mm and pinchoff voltages in the range of 3 V.