Excess Carriers In Semiconductors Research Articles

An improved version of the Haynes–Shockley experiment with electrical or optical injection of the excess carriers

The Haynes–Shockley experiment allows direct measurements of the drift mobility, of the diffusion coefficient, and of the recombination lifetime of excess carriers in semiconductors. In order to obtain easier and more accurate measurements in a didactic laboratory, we designed a new setup for this experiment that uses electrical or optical injection of the excess carriers.

Behavior of photoconductivity transients due to multiple trapping by a Gaussian distribution of localized states

The decay of excess carriers in semiconductors was analyzed under conditions of multiple trapping by a Gaussian distribution of subband gap states and recombination. Numerical solutions to the rate equations involving multiple trapping in subband gap states and recombination indicate that a power-law decay is observed only under limited conditions. The concept of an optimally filled energy level for which a ratio of the trapping time to the release time has a minimum is introduced for the Gaussian distribution. We showed that the position of the Fermi level may limit the portion of the distribution that can be effective in the decay. The results provide an explanation for the nonlinear temperature dependence of the exponential term ${\ensuremath{\alpha}}_{1}$ that is sometimes observed experimentally.

Evidence for the role of the surface potential and native oxide on thermal properties of crystalline Si

Thermal properties of crystalline Si have been studied using the photopyroelectric (PPE) technique in the temperature range 100–300 K. It has been observed that the generation and propagation of the thermal waves in Si depends upon the thermal history of the sample. The native amorphous silicon dioxide layer on Si and the surface potential affect the propagation of the thermal waves and this effect is not reversible in the temperature range 150 K<T<260 K. It is observed that the contactless PPE technique can also be used to study recombination processes of excess carriers in semiconductors.

Recombination-induced defect heating and related phenomena

The theory of recombination-induced heating is presented. The main mechanisms involved in the excitation and relaxation of local vibrations of defects are considered. It is shown that the high-energy 'tail' of the defect distribution function by vibration energies dramatically increases in the presence of excess carriers in semiconductors due to multiphonon recombination via deep defects. An example of numerical calculation of the defect distribution function is given. The theory is used to calculate the rate of recombination-stimulated reactions and to interpret experimental data on inelastic sputtering of solid surfaces by ion bombardment. It is shown that the defect heating should change the non-radiative recombination rate in the case of highly doped semiconductors or large concentrations of excess carriers.

New light modulation device: optical transistor

The plasma reflectivity edge in the infrared reflectivity spectrum measured on a narrow-gap semiconductor HgCdTe has been found to be very sensitive to the variation of carrier concentration under certain circumstance, based on which a new way of infrared modulation is studied, where the estimated modulation gain in power is impressively high. Thus, infrared radiation in far- and mid-infrared can be effectively modulated by electromagnetic waves with shorter wavelengths, and hence a less sensitive room-temperature infrared detector could be as sensitive as the existing cooled infrared detectors. The suggested new optoelectronic device, which can be termed an optical transistor, working with light beams instead of electronic currents, is quite promising for fiber communication and infrared detection as well as for investigating the relaxation processes of excess carriers in semiconductors. The detectivity for the plasma-edge detector, which is a detector equipped with an optical transistor, is calculated.

Application of infrared reflectivity to the study of the relaxation process of excess carriers in semiconductors

Based upon the study of an infrared reflectivity spectrum of a semiconductor, a measurement has been put forward which constitutes a versatile tool for non-contact and non-destructive characterization of the relaxation processes in both film and bulk materials by its novel properties.

First-overtone response in modulated photoluminescence emission in silicon at room temperature.

At sufficient photoexcitation, radiative relaxation of excess carriers in semiconductors becomes quadratically dependent on the excess carrier density and can lead to photoluminescence emission at the first overtone of the modulation frequency of the incident light. We have observed, for the first time, a first-overtone component in amplitude-modulated photoluminescence in silicon at room temperature and describe its origin.

Decay of excess carriers in semiconductors

The initial and final stages of decay of excess carrier densities in a semiconductor containing one or more levels of monovalent centres are investigated in terms of the carrier transition rates. A relation for the time dependent excess free carrier lifetimes is found for the one-level model in the initial stage of decay. Solutions for the final stage of decay are pictured in kinetic diagrams. On the basis of the kinetic diagrams the temperature dependence of is derived for the case of the one-level model. Conditions are found, under which the solution of the many-level model reduces to the solution of the one-level model. Das Anfangs- und Endstadium des Abklingens der überschüssigen Ladungsträgerkonzentration in Halbleitern, die ein oder mehrere Terme von monovalenten Zentren enthalten, werden mit Hilfe der Ladungsträgerübergangsraten untersucht. Für die zeitabhängigen Lebensdauern wird eine Beziehung für das Anfangsstadium des Abklingens im Ein-Term-Modell abgeleitet. Die Lösungen für das Endstadium des Abklingens werden in kinetischen Diagrammen veranschaulicht. Mit Hilfe der kinetischen Diagramme wird die Temperaturabhängigkeit von für das Ein-Term-Modell abgeleitet. Es werden gewisse Bedingungen gefunden, unter denen die Lösung des Mehr-Term-Modells in die Lösung des Ein-Term-Modells übergeht.

THE PHASE-SHIFT LIFETIME OF EXCESS CARRIERS IN SEMICONDUCTORS UNDER SINUSOIDAL INJECTION

This paper analyzes, with single energy-level recombination-centre model, the phase-shift lifetime of excess carriers in semiconductors under sinusoidal injection. Hence are obtained the difference and sameness between phase-shift lifetime and static state lifetime as well as transient state lifetime:1. The phase-shift lifetime in relation with the injection frequency decreases as the frequency increases.2. Under low frequency injection, the phase-shift lifetimes of electrons and holes are the same and equal to transient state lifetime.The conditions of low frequency injection are discussed in this paper.

Summer Programs

A program in experimental solid‐state physics will be offered from June 22 to July 24 by the Metallurgy and Electrical Engineering Departments of the Massachusetts Institute of Technology, under the direction of Professors Simon C. Moss and Roy Kaplow. Intended primarily for faculty members in the materials sciences who wish to obtain first‐hand experimental experience, the course will deal with x‐ray diffraction, crystal growth, infrared spectroscopy, magnetic resonance, galvanomagnetic effects, excess carriers in semiconductors, ferroelectricity, thermal properties, superconductivity, and the Mössbauer effect. In addition to laboratory work, the program will include background lectures, references to selected literature, and tours of several solid‐state experimental facilities at MIT. Limited funds will be available for the support of participants and their families. Further information and application blanks can be obtained from Professor Roy Kaplow, Room 16–502, Massachusetts Institute of Technology, Cambridge 39, Mass. The deadline for receipt of applications is April 15.

Spontaneous and Stimulated Recombination Radiation in Semiconductors

Spectral line shapes of the radiation produced by band-to-band recombination of excess carriers in semi-conductors are calculated under the assumption that the momentum matrix element is the same for all initial and final states, i.e., that there is no momentum selection rule. The peak of the stimulated radiation falls at a lower photon energy than does the peak of the spontaneous radiation, except when $T=0$\ifmmode^\circ\else\textdegree\fi{}K. Some numerical results are given for simple parabolic bands, specifically for the case of electron injection into $p$-type GaAs, and are used to deduce the temperature dependence of the forward current which is necessary to maintain a fixed gain in the active region of a diode. The result is closely related to the temperature dependence of the threshold current in an injection laser, and gives reasonable agreement with experiment. The effect of a conduction band tail is briefly considered.

Decay of Excess Carriers in Semiconductors. II

Decay of Excess Carriers in Semiconductors. II

One-dimensional overlap functions and their application to Auger recombination in semiconductors

The theoretical lifetime of excess carriers in semiconductors limited only by the Auger recombination mechanism previously discussed by the present authors, depends on a temperature-independent parameter. This involves certain overlap integrals. They are of the form ∫ u *(k 1 , r) u (k 2 , r) dr, where the u ’s are the modulating parts of Bloch wave functions. The integrals are calculated in this paper on the basis of a Kronig-Penney model. The value of the parameter obtained is shown to be rather insensitive to many details of the model used. When the value found is inserted into the previously published theory of lifetimes in InSb, very good agreement is obtained with the more detailed experimental results which have recently become available. This strongly suggests that the dominant recombination mechanism in InSb at elevated temperatures has been identified. A more general analysis of the properties of the overlap integrals is also given in this paper.

Principles of Semi-Conductor Device Operation

By A. K. Jonscher London : G. Bell & Sons Ltd. Pp. viii + 168. Price 30s. In spite of its clumsy and forbidding title this is a good book. It is concerned primarily with the subject of injection, decay and transport of excess carriers in semiconductors.

Further Consideration of Bulk Lifetime Measurement with a Microwave Electrodeless Technique

A new method for measurement of the lifetime of excess carriers in semiconductors is described. Using a steady light source and measuring changes in microwave power absorption as a function of position of the sample in a waveguide, bulk lifetime can be determined. Measurements described here were made at 9600 mc. The new technique offers the following advantages: First, the method does not require electrode attachments, thus making the preparation of the samples less difficult and the actual experiment less subject to error due to non-ohmic contacts. Second, the effects of surface recombination are made less important, thus giving a greater assurace of the evalaution of bulk lifetime.

The Effect of an Electric Field on the Decay of Excess Carriers in Semiconductors

The Effect of an Electric Field on the Decay of Excess Carriers in Semiconductors

Decay of Excess Carriers in Semiconductors

A discussion is given of the nonlinear differential equations which govern the decay of excess carriers with arbitrary densities. The form of decay is explored for situations where the Fermi level is in the same half of the energy gap as the recombination level; criteria are established for both strong and weak trapping in addition to recombinative action. Analytic results are augmented and illustrated by numerically computed decay curves for a variety of circumstances. The separate solutions for holes and electrons are combined to show various kinds of behavior for photoconductive lifetime.

Recombinaison sur les Pièges à deux Niveaux dans les Semi-Conducteurs†

ABSTRACT The derivation of the recombination statistics of excess carriers in semiconductors through a Hall-Shockley-Read mechanism with two non-independant levels in the forbidden gap is given. Two examples are outlined : low-level injection lifetime and generation rate for p-n junction charge space.

Recombination in Semiconductors

Excess carriers in semiconductors recombine either by direct recombination of electrons and holes, or through the intermediacy of recombination centers. The latter process is the one observed in silicon and germaniun. Various impurity atoms, dislocations, vacancies, and interstitials are known to act as recombination centers. The capture rates associated with these imperfections vary over a wide range depending on their state of charge. Recombination at the surfaces is described in terms of a similar model in which surface states replace the recombination centers present in the bulk. The surface recombination velocity measures the density and capture properties of these states. A given center can act as a recombination center or a trap depending on the relative magnitude of the capture cross sections for electrons and holes. This paper reviews the analytical treatments of the different processes as well as specific experimental results.

Recombination of Excess Carriers in Semiconductors

The recombination of excess carriers in semiconductors is discussed on the basis of a model in which the recombination occurs through multiple-levels. The theory is extended to apply to germanium. The dependence of carrier lifetime on temperature in most of pure n -type germanium samples can be explained by introducing two sets of traps, recombination centers ( E C - E r =0.30eV) and hole trapping centers ( E t - E V =0.30eV), in our temperature range. However, the minority carrier lifetime of samples containing comparatively high dislocation density (10 4 –10 5 /cm 2 ) is shown to vary with the dislocation density, and the results is expressed in terms of two lifetimes: τ d , that associated with random dislocations, and τ b , that due to the recombination centers of an undetermined origin. It is also shown that anomalous temperature dependence of the steady-state photoconductivity of high-resistivity p -type nickel doped germanium can be interpreted by assuming that two acceptor levels of nickel atom ar...