Temperature, electric field, and doping dependent mobilities of electrons and holes in semiconductors

A new formula for electron and hole mobilities in semiconductors is presented. Although empirical, it is accurate and widely applicable to a number of semiconductors, such as Si, Ge, GaAs, InP, etc. The formula is simple, and yet predicts temperature and field dependence of electron and hole mobilities very well. To our knowledge, the present model is more general than any other model (both empirical and theoretical) available in the literature. Because of very simplistic nature, it promises to be highly useful for analytically modeling the current-voltage characteristics of transistors.     

Methodology for calculating turn-off transient of photoconductive circuit elements in picosecond optoelectronics

A methodology for calculating the transient following sudden removal of photon or mass-particle excitation is developed for semiconductor devices in which high hole-electron recombination rates, rather than short transit times, yield picosecond response time. We suggest the name photoconductive circuit element (PCE) for these optoelectronic transducers to emphasize their potential application to diverse circuit and system functions. The device consists of a nearly intrinsic active region that contains extremely high concentrations of deep-level states acting as recombination centers. Regions of semiconductors highly doped with shallow donor or acceptor atoms connected to metallic contacts border this active region. In calculating the turnoff transient, we set forth criteria that define nearly ideal ohmic-contact systems and the quasi-neutrality regime of the intrinsic region. If these criteria are met, the turn-off transient becomes a problem in photoconductive decay. For incremental variations in the electron and hole quasi-Fermi voltages much less than the thermal voltage, two characteristic times, assigned to each recombination-center energy level, rather than a single lifetime, describe electron-hole recombination. A computer algorithm accounting for incremental variations within suitably small time intervals then enables calculation of observables that may vary by many orders of magnitude, InP:Fe photoconductive circuit elements containing eight different Fe concentrations, excited by 780 and 600 nm laser-light pulses and 6 MeV electron pulses, showed a (1/e)-fall-time versus Fe-concentration in general accord with results calculated by the methodology. The capture cross sections and the energy distribution of the recombination-center energy levels receive attention. The InP:Fe transducers showed (1/e)-fall-times in the sub- 100-ps regime.     

GaInAs junction FET with InP buffer layer prepared by selective ion implantation of Be and rapid thermal annealing

GaInAs JFETs were fabricated on VPE-grown GaInAs layers. The pn junctions have been realised with Be ion implantation and rapid thermal annealing. The devices show a high transconductance of 130 mS/mm and an electron saturation velocity of 1.8 × 107 cm/s. Channel mobilities measured at the complete device are as high as 6800 cm2/Vs. These excellent device properties are due to the use of an undoped InP buffer layer which avoids the diffusion of Fe from the substrate into the active layer. The data were supported by S-parameter measurements which gave a frequency limit of 20 GHz for gate dimensions of 1.6 by 200 ?m2.     

Influence of the dislocation density on the performance ofheteroepitaxial indium phosphide solar cells

The authors point out that heteroepitaxial indium phosphide solar cells developed to date have low efficiency due to misfit dislocations. Dislocations act as recombination centers and strongly influence the solar cell performance. Calculations have been made to study the dependence of heteroepitaxial InP solar cell efficiency on dislocation density. The effects of surface recombination velocity and cell emitter thickness are also considered. Calculated results are compared with the available experimental results on representative InP solar cells. It is shown that heteroepitaxial InP cells with over 20% AM0 efficiency could be fabricated if dislocation density can be reduced to <10⁵ cm^-2 and the surface recombination velocity reduced to <10⁵ cm/s     

Influence of iron content on electrical characteristics and thermal stability of LEC indium phosphide

The Hall mobilities (conductivity type) measured on many Fe-doped InP wafers have been used as a parameter for material assessment. The samples can essentially be assigned to three groups. Interpretation of the experimental data is given for each group of samples. Furthermore, we report the results of electrical measurements on annealed InP and show the kind of correlation existing between the electrical characteristics of as-grown and annealed InP. Finally, we report a study on the homogeneity of Fe-doped InP on a macroscale. It is seen that the experimental resistivity profiles along the wafer diameters are a function both of the Fe and shallow inpurities profiles.     

A numerical calculation of auger recombination coefficients for InGaAsP/InP quantum well heterostructures

Auger recombination coefficients are calculated numerically for InGaAsP/InP quantum well heterostructures. In narrow quantum wells, the quasi-threshold and thresholdless mechanisms mainly contribute to the Auger recombination coefficient. For the processes involving two electrons and a heavy hole (CHCC) or an electron and two heavy holes with a transition of one of the holes to the spin-orbit split-off band (CHHS), the Auger recombination coefficients depend on temperature only slightly in a wide temperature range. The dependence of the Auger coefficient on the quantum well width is analyzed and found to be nonmonotonic.     

Electrical measurement of electron and hole mobilities as afunction of injection level in silicon

The first experimental method to separately measure the hole and the electron mobilities as a function of the injection level is presented. The carrier mobilities are extracted from impulsive measurements of the resistance associated with a n⁺-ν-n ⁺ (p⁺-π-p⁺) structure, where the conductivity of the intermediate layer is controlled by the injection of an incorporated p-n junction diode. Two-dimensional numerical simulation is used to assess the accuracy of the proposed measurement technique. Experimental results obtained at room temperature on both n-type and p-type materials are presented and compared to existing analytical mobility models     

A virtual self-aligned process for n-channel InP IGFET's (or MISFET's)

A virtual self-aligned process for fabricating IGFET's (or MISFET's) has been developed. Devices fabricated on semiinsulating InP substrates using this process show: (i) square-law characteristics, (ii) an inverse-relationship between transconductance and gate length, and (iii) high surface channel electron mobilities on the order of 1000 cm²/v.sec.     

Surface recombination currents in "Type-II" NpN InP-GaAsSb-InP self-aligned DHBTs

Surface recombination effects are studied in non-passivated non-self-aligned and self-aligned NpN InP-GaAsSb-InP double heterostructure bipolar transistors (DHBTs) down to submicrometer emitter dimensions, and over current densities ranging from 10 A/cm/sup 2/ to 100 kA/cm/sup 2/. The present study is motivated by the drive to scale InP DHBTs for higher speeds and integration densities. Self-aligned InP-GaAsSb-InP DHBTs are characterized by weak emitter size effects (ESEs), and periphery recombination currents are found to be very nearly identical to published results for InP-GaInAs SHBTs despite the major differences in emitter junction band alignments ("type-II" versus "type-I") and injection mechanisms (thermal versus hot electron injection). The correspondence of measured periphery currents in both systems indicates that ESEs are dominated by a mechanism common to InP-GaAsSb and InP-GaInAs devices: this requirement is fulfilled by the direct electron injection from the InP emitter mesa sidewalls onto the extrinsic base surface. Consideration of band alignments and surface depletion effects at the extrinsic base surface is used to explain the commonality of emitter size effects in InP-GaAsSb and InP-GaInAs devices.     

Measurement of Deep Energy Level in InP：Fe by the Method of OTCS

We have measured the deep energy level of the InP:Fe which is semi -insulator through the method of OTCS.The effect of light intensity on OTCS measurement is mainly discussed. There are electron trap of ET=0.034 eV and hole trap of ET=1.13 eVin InP:Fe under the strong light and low temperature .The location of the OTCS peak of electron trap(ET=0.34 eV)moves towards the direction of high temperaturer,when the light intensity was increased,ET is different under different light intensity .It is corrected in terms of theory that the stuff ratio of the deep energy level is affected by the light intensity. The experiments show that the error is decreased greatly with the correction.     

Minority-carrier injection into polysilicon emitters

The hole transport equation is solved for a polysilicon emitter of a bipolar transistor. The recombination at the grain boundaries as well as at the poly-monosilicon interface is considered. An effective surface recombination velocity is defined and calculated as a function of surface state density and number of grain boundaries. A comparison between the injected hole current into the diffused region of both an Al contact and a polysilicon-silicon emitter is given as a function of surface state density for different numbers of grain boundaries. Also the injected current is calculated for different values of junction depth and surface concentration.     

Electron and hole mobilities in inversion layers on thermally oxidized silicon surfaces

Extensive measurements of electron and hole mobilities in inversion layers on thermally oxidized silicon surfaces were performed using the field effect conductance technique. It was found that both electron and hole mobilities are practically constant and approximately equal to one half of their respective bulk values up to a surface field of about 1.5 × 10⁵volts/cm, corresponding to about 10¹²electronic charges/cm²induced in the silicon. At higher fields the inversion layer mobilities begin to decrease slightly. The temperature dependence of inversion layer mobilities follows a T^-1.5rule at the upper range of the interval -196 to 200°C, indicating a scattering mechanism similar to lattice scattering. This observation is further supported by the lack of a significant effect of an order-of-magnitude variation in the bulk impurity concentration (10¹⁵- 10¹⁶cm³) on the inversion layer mobilities. No significant effect of structural and geometrical parameters (such as channel length and shape, oxide type and thickness, and surface charge density) was found on the inversion layer mobilities.     

Carrier mobility in MOSFETs fabricated with Hf-Si-O-N gate dielectric, polysilicon gate electrode, and self-aligned source and drain

A study of electron and hole mobilities for MOSFET devices fabricated with Hf-Si-O-N gate dielectric, polysilicon gate electrodes and self-aligned source and drain is presented. High effective electron and hole mobilities, 250 cm/sup 2//V/spl middot/s and 70 cm/sup 2//V/spl middot/s, respectively, were measured at high effective field (>0.5 MV/cm). The NMOSFETs have an equivalent oxide thickness (EOT) of 1.3 nm and the PMOSFETs have an EOT of 1.5 nm. The effect of interface engineering on the electron and hole mobilities is discussed.     

Pseudomorphic AlInP/InP heterojunction bipolar transistors

Novel InP-based heterojunction bipolar transistors (HBTs) using an AlInP pseudomorphic emitter, together with an InP base and collector, have been fabricated. By using InP as both base and collector, the advantage of high electron velocity and high breakdown field of InP collectors are obtained without the problem associated with the energy barrier between the more standard InGaAs/InP base and collector heterojunction. Epitaxial layers were grown by gas-source molecular beam epitaxy (GSMBE). The 200 Å pseudomorphic emitter had an aluminium fraction of 15%, sufficiently suppressing hole injection from the base. The DC gain for 40×40 μm² devices reached 18. The breakdown voltage BV_CEO of 10 V is an improvement over devices with InGaAs base and collector layers     

Explaining the dependences of the hole and electron mobilities inSi inversion layers

In this work the hole surface roughness-limited mobility in Si MOSFETs is investigated. Based on full-band Monte Carlo simulations and on an equivalent relaxation-time numerical model, we show that the differences between hole and electron experimental mobilities are not due to any peculiar physics of the valence band. They can be instead accounted for by a suitable shape of the power spectrum describing the surface roughness. The new power spectrum explains the experimental dependences of both electron and hole mobilities using the same surface roughness parameters. Finally the spatial features of the roughness described by the new spectrum are discussed and compared to those represented by Gaussian and exponential auto-covariance functions     

Surface-recombination-free InGaAs/InP HBTs and the base contact recombination

Surface-recombination-free InGaAs/InP HBTs with graded base have been demonstrated. The HBTs were passivated by ammonium sulfide. The current gain of the nonself-aligned HBTs was independent of the emitter periphery, indicating that the surface recombination was removed by the passivation. For the self-aligned HBTs, the current gain was still dependent on the emitter periphery after the passivation due to the base contact recombination. A surface leakage channel has been identified to result in a significant increase in the base contact recombination. The passivation has two effects: one is the surface recombination velocity reduction and the other is the surface leakage channel elimination.     

Design and characteristics of InGaAs/InP composite-channel HFET's

A design for composite-channel structures consisting of an InGaAs channel and an InP subchannel for use as heterostructure field-effect transistors is presented for the first time. This novel channel structure takes advantage of both the high drift velocity and low impact ionization of InP at high electric fields as well as the high electron mobility of InGaAs at low electric fields. It is shown that the doping density of the InP subchannel is the key parameter to realize the advantages of the composite channel. A very high transconductance of 1.29 S/mm and a current gain cutoff frequency of 68.7 GHz are achieved with 0.6 and 0.7 /spl mu/m gates, respectively. The average velocity of electrons in the composite channel is 2.9/spl times/10/sup 7/ cm/s. The devices have no kink phenomena in their I-V characteristics possibly due to low impact ionization in the InP subchannel.<>     

Role of Interface Chemistry in Opening New Radiative Pathways in InP/CdSe Giant Quantum Dots with Blinking‐Suppressed Two‐Color Emission

InP/CdSe core/thick‐shell “giant” quantum dots (gQDs) that exhibit blinking‐suppressed two‐color excitonic emission have been synthesized and optically characterized. These type II heterostructures exhibit photoluminescence from both a charge‐separated, near‐infrared type II excitonic state, and a shell‐localized visible‐color excitonic state. Infrared emission is intrinsic to the type II QD, while visible emission can either be eliminated or enhanced through chemical modification of the InP surface prior to CdSe shell growth. Single‐QD photoluminescence measurements confirm that the dual color emission is from individual nanocrystals. The probability of observing dual emission from individual QDs and the extent of blinking suppression increases with shell thickness. Visible emission can be stabilized by the addition of a second shell of CdS, where the resulting InP/CdSe/CdS core/shell/shell nanocrystals afford the strongest blinking suppression, determined by analysis of the Mandel Q parameter. Transient absorption spectroscopy verifies that dual emission arises when hole relaxation from the shell to the core is impeded, possibly as a result of enhanced interfacial hole trapping at F^? or O^2? defect sites. Electron–hole recombination in the shell then competes with slower type II recombination, providing a different mechanism for breaking Kasha's rule and allowing two colors of light to be emitted from one nanostructure.     

InP中皮秒快速现象

利用测量瞬态反射谱的方法，探索了掺硫、铁、锌以及非掺杂的ＩｎＰ中载流子寿命，观察到非掺杂ＩｎＰ中载流子寿命最长约６０ｐｓ，掺锌ＩｎＰ中载流子寿命３８ｐｓ居中，掺硫和掺铁的寿命最短约１ｐｓ掺硫、铁和锌的ＩｎＰ中载流子寿命下降，是由于掺杂引入了复合中心，这一结果已被喇曼光谱所证实。     

Hole and electron mobilities in heavily doped silicon: comparison of theory and experiment

Most device models for npn or pnp transistors assume that hole (electron) mobilities in n-type and p-type silicon are equal. Partial-wave phase shift calculations for the contributions of carrier-dopant ion scattering to the carrier mobilities lead to unequal minority hole (electron) and majority hole (electron) mobilities at the same doping density. These calculations are valid over the doping range of 2 x 10¹⁹ to 8 x 10¹⁹ cm⁻³ in n-type and p-type silicon and contain the assumptions that the holes and electrons move in isotropic parabolic energy bands and are scattered by the screened Coulomb potentials of the dopant ions. When the effects of carrier-acoustic phonon and carrier-carrier scatterings are included, these calculations agree to within the spread of experimental value for the majority mobilities reported in the literature. This agreement is a substantial improvement by factors of 2–4 over the results of earlier theories such as first order Born and nondegenerate theories. The results of this work, particularly the inequality of minority and majority carrier mobilities, have implications for the modeling of both bipolar and field effect transistors.