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We introduce a simple and sensitive technique for measuring extremely low solubilities with a small sample size and small solvent volume. This technique involves measuring the decrease in the thickness of a supported thin film after exposure to a drop of known volume of solvent and removal of the solution. The feasibility of measuring very small changes in film thickness directly translates to the ability to measure extremely low solubility while at the same time using only μL of solvent. We apply the technique to the case of polystyrene with Mw values in the range 2500 g/mol to 22200 g/mol in alkane solvents and show that we can easily measure a solubility of 0.1 g/L using only 1 $ \mu$ g of material and 3 $ \mu$ L of solvent for each sample.

The demonstration, over 20 years ago, of an organic–inorganic heterojunction (OI HJ) device along with investigations of the growth and physical properties of the archetypal crystalline molecular organic semiconductor 3, 4, 9, 10 perylenetetracarboxylic dianhydride are discussed. Possible applications of OI HJ devices are introduced and the dramatic change in conductive properties of these materials when exposed to high-energy ion beams is described. The past and future prospects for hybrid organic-on-inorganic semiconductor structures for use in electronic and photonic applications are also presented.

We demonstrate that ordered microlens arrays with 10 μm diam poly-dimethyl-siloxane lenses attached to glass substrates increase the light output of organic light emitting devices (OLED) by a factor of 1.5 over unlensed substrates. The lenses, which are considerably smaller than, and not aligned to the OLEDs, outcouple light that is emitted outside of the escape cone of the substrate. We show that an electrophosphorescent device based on a fac tris(2-phenylpyridine)Iridium (Ir(ppy)3) doped emitting layer has its external quantum efficiency increased from 9.5% using a flat glass substrate, to 14.5% at low current densities using a substrate with microlenses. No change in the emission spectrum is observed for different viewing angles using the lens arrays.

Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is shown to be a means for achieving efficient and bright full-color displays. In Paper I, we addressed stacked OLED (SOLED) design and fabrication principles to optimize emission colors, operating voltage, and efficiency. Here, we present results on two different (metal-containing and metal-free cathode) SOLED structures that exhibit performance suitable for many full-color display applications. The operating voltages at 10 mA/cm2 (corresponding to video display brightnesses) are 6.8, 8.5, and 12.1 V for the red (R), green (G), and blue (B) elements of the metal-containing SOLED, respectively. The respective subpixel luminous efficiencies are 0.53, 1.44, and 1.52 cd/A, and the Commission Internationale de L’Eclairage (CIE) chromaticity coordinates are (0.72, 0.28), (0.42, 0.56), and (0.20, 0.22). In the high transparency metal-free SOLED, an insulating layer was inserted between the two upper subpixels to allow...

We present a study of optically pumped waveguide and microcavity lasers based on vacuum-deposited thin films of small molecular weight organic semiconductors. Lasing action in waveguide lasers is characterized by high output peak power (50 W), high differential quantum efficiency (70%), low lasing threshold (1 μJ/cm2), and long operational lifetime (>106 laser pulses at 100 times the threshold pump power). Microcavity laser characteristics include 3 W peak output power, 300 μJ/cm2 lasing threshold, and lifetimes of >106 pump laser pulses (operating at 6 times the threshold power). We demonstrate wavelength variability from 460 to 700 nm by changing the composition of the organic films. The confinement of excitations on the dopant molecules leads to quantum dot-like behavior such as high temperature stability of the lasing threshold, output power, and emission wavelength in the temperature range from 0 to 140 °C. The linewidth of laser emission from microcavity structures is found to be 0.2±0.1 A and is tr...

Ultraviolet (UV) optical pumping followed by fluorescence wavelength downconversion of thin film organic light emitting materials deposited directly on the surface of Si p‐n junction diodes is found to be an accurate and rapid means to determine the film internal fluorescence efficiency. By measuring the photoresponse of the Si detectors in the UV, we find that the organic light emitting films of aluminum tris‐(8‐hydroxyquinoline) (Alq3), N,N′‐diphenyl‐N,N′‐bis‐(3‐methylphenyl)‐ 1,1′‐biphenyl‐4,4′‐diamine, and bis‐(8‐hydroxyquinaldine)‐chlorogallium (Gaq2′Cl), have internal fluorescence efficiencies of 0.30±0.05, 0.35±0.03, and 0.36±0.03, respectively. It has also been found that the organic films can be grown to a thickness which optimizes UV light conversion and can, at the same time, serve as antireflection coatings in the visible spectral region, thereby resulting in enhanced Si photodiode sensitivity extending from the UV to the infrared.

We demonstrate high open circuit voltage (Voc) organic photovoltaic (PV) cells that incorporate two, three, or five stacked, thin heterojunctions (HJs) consisting of Cu-phthalocyanine as a donor, and 3,4,9,10 perylenetetracarboxylic bis-benzimidazole as an acceptor. Ultrathin (∼5 A average thickness) layers of Ag clusters are placed between each HJ to serve as recombination centers for unpaired charges that are photogenerated in the device’s interior. High power conversion efficiencies with high Voc have been demonstrated in cells containing up to five optically active HJs and four interstitial metallic recombination regions. The power conversion efficiencies of the two and three HJ cells under one sun, AM 1.5 illumination are ηp=2.5±0.1% and ηp 2.3±0.1%, with Voc=0.93±0.05 and 1.20±0.05 V, respectively. These values of ηp are more than twice that of a comparable single-junction cell based on the same materials, where ηp=1.1±0.1%.

In the standard architecture for optical communications receivers there are typically three basic elements, a photodetector, a pre-amplifier, and a filter. If the signal is frequency multiplexed, there must be an additional mixing stage to separate the different incident optical channels. Sensitivity and gain are most critical for these elements since the signal is weakest and most susceptible to noise at the receiver front end. In commercial receivers, the photodetector and mixer are separate from the pre-amplifier and must be integrated by hybrid techniques. Interconnections between the pre-amplifier and the other components frequently require complex matching networks or interconnection schemes which introduce unwanted noise while reducing reliability. We have designed and tested a high sensitivity p-i-n/JFET, monolithically integrated photoreceiver which incorporates a p-i-n photodiode and a voltage tunable transimpedance preamplifier for 1.3-1.55 pm optical fiber communication. This design allows us to monolithically mix an optical signal with an electrical signal for use in applications such as frequency demultiplexing or coherent detection. Comparison of our results with alternative mixer technology indicates good efficiency with low signal distortion.

Organic photodetectors incorporating an ultrathin (⩾5 A) donor–acceptor alternating multilayer stack as the optically active region exhibit external quantum efficiencies of 75% across the visible spectrum, and have subnanosecond response times. Photogenerated excitons efficiently dissociate into free electrons and holes by rapid charge-transfer across the several closely spaced organic-layer interfaces. The dependence of the quantum efficiency on applied voltage and layer thickness suggests that escape of photogenerated carriers from potential wells formed by the multilayers due to tunneling prior to recombination leads to the high efficiencies observed. The impulse response of the highest-bandwidth devices is characterized by a full width at half maximum of (720±70) ps. The performance of these devices makes them a useful building block for molecular organic photonic integrated circuits.

Interface charge densities and conduction‐band offset energies for liquid‐phase epitaxially grown n‐N isotype In0.53Ga0.47As/InP heterojunctions have been measured using capacitance‐voltage methods. Extremely low interface charge densities have been obtained in some samples, and they are found to be independent of both the measurement temperature and the magnitude of lattice mismatch. Our samples show a clear peak and notch in the apparent free‐carrier concentration profile at temperatures as low as 83 K. This is in contrast to results reported previously where the notch, due to the carrier depletion at the heterojunction, was observed to vanish at low temperature. An electron trap has been identified in one of the samples. The trap is uniformly distributed within the bulk of the In0.53Ga0.47As layer at a density of 5×1014 cm−3. In spite of the presence of this relatively low density defect, the heterojunctions grown for this study apparently have considerably lower interface defect densities than observe...

Using electro-optical pump and probe measurements, we studied optical properties of a thin film of tris-(8-hydroxyquinoline) aluminum (Alq3) doped with DCM2 laser dye under pulsed injection currents as high as 300 A/cm2. Pump-induced transparency and absorption were observed in the spectral ranges of 570–610 nm and 620–705 nm, respectively. We attribute these optical effects to molecular polarons formed under electrical excitation. Polaron absorption dominates the optical properties of electrically pumped Alq3:DCM2 films in the spectral range where optical gain is anticipated (i.e., from 630 to 700 nm). Polaronic effects may present a significant obstacle for realization of organic diode lasers based on this material system.

We report a semitransparent, two-color, stacked organic light-emitting device (SOLED) with high efficiency, low drive voltage, and minimal color distortion. The SOLED emits light from both device surfaces. The external quantum efficiencies of the green and red stacked elements are 1% and 0.4%, respectively, where only the photons emitted from the substrate surface are collected. The drive voltage for the top stack element is decreased to ∼12 V by using a modified indium tin oxide thin film deposition process. Color distortion and angular dependence of the emission spectra are minimal.

We model a three-color stacked organic light emitting device (SOLED) and determine the influence of microcavity effects on the color saturation of the layered, light emitting elements. Using the model, we design and demonstrate a SOLED with good color saturation and minimal viewing angle effects. The Commission Internationale de L’Eclairage chromaticity coordinates for the red, green, and blue subpixels of the SOLED are (0.68, 0.32), (0.32, 0.53), and (0.14, 0.19), respectively. The full color SOLED opens a path to full color, lightweight displays utilizing vertically stacked color elements to maximize the resolution and aperture ratio of the display.

We introduce a class of low-reflectivity, high-transparency, nonmetallic cathodes useful for a wide range of electrically active, transparent organic devices. The metal-free cathode employs a thin film of copper phthalocyanine (CuPc) capped with a film of low-power, radio-frequency sputtered indium tin oxide (ITO). The CuPc prevents damage to the underlying organic layers during the ITO sputtering process. We present a model suggesting that damage-induced states at the cathode/organic film interface are responsible for the electron injection properties of the contact. Due to the low contact reflectivity, a non-antireflection-coated, metal-free transparent organic light-emitting device (MF-TOLED) is demonstrated with 85% transmission in the visible, emitting nearly identical amounts of light in the forward and backscattered directions. The MF-TOLED performance is found to be comparable to that of conventional TOLEDs employing a more reflective and absorptive cathode consisting of a semitransparent thin fil...

Lasing at 460, 485, and 510 nm is demonstrated in optically pumped, vacuum-deposited amorphous thin films of a carbazole derivative doped with Coumarin 47, perylene, and Coumarin 30, respectively. Efficient, nonradiative Forster energy transfer between host and dopant organic molecules results in low lasing thresholds (5 μJ/cm2), high differential quantum efficiencies (15%), high peak output powers (20 W), and long operational lifetimes (>105 pulses at 100 times the threshold power).

Characteristics of lasing in optically pumped, vacuum deposited organic semiconductor thin films of tris-(8-hydroxyquinoline) aluminum doped with DCM laser dye are studied as a function of DCM concentration and ambient temperature. In contrast to inorganic laser diodes, the lasing wavelength, output power, differential quantum efficiency, and threshold pump energy of organic lasers are found to be independent of temperature in the range from 0 to 140 °C. In addition, no degradation in laser performance was observed at temperatures approaching 160 °C.

We discuss the growth of thin films of the organic salt, 4′‐dimethylamino‐N‐methyl‐4‐stilbazolium tosylate (DAST) by the novel process of organic vapor phase deposition (OVPD). These films show long‐range structural ordering and very intense second harmonic generation efficiencies (SHG) significantly greater (when normalized for thickness) than that of randomly oriented pure DAST powders. This is the first demonstration of such intense SHG radiation and long‐range ordering for a thin film sample of a nonlinear organic salt. Furthermore, this work suggests that OVPD represents a general technique for growing thin films of highly polar, nonlinear optical materials such as DAST.

Photoluminescence of 1.3 μm wavelength strained multiple quantum well InGaAsP/InP laser structures has been used to understand the excess carrier redistribution between the quantum well and waveguide regions at a high level of excitation. A model is developed to describe the experimental results. The model suggests that space charge barriers play a significant role in the electron confinement in quantum wells at the high excitation range typical of laser diode operation.

Results are presented from polymer/molecular organic heterostructure light emitting diodes composed of a layer of the conjugated conducting polymer poly(p‐phenylene vinylene) (PPV), and a layer of fluorescent molecular compound tris(8‐hydroxy) quinoline aluminum (Alq). The external quantum efficiency of these heterostructure LEDs is ∼0.1%, which is over one order of magnitude higher than that of simple PPV LEDs. The electroluminescence (EL) spectra indicate that both materials in the device emit comparable amounts of light. The dependence of the EL spectra on the layer thicknesses and its independence on bias suggest that neutral excitons are formed in the Alq, far from the PPV/Alq interface, and subsequently diffuse into the PPV layer.

We present a systematic analysis of the relationship between the photoluminescence (PL), light emitting device electroluminescence (EL), and conducting properties of a series of metalquinolates, Mq3, where M is a metal (Al, Ga, In, or Sc), and q3 is tris‐(8‐hydroxyquinoline). We compare the solution and thin film PL quantum yields and spectra of each quinolate with the EL quantum efficiencies of organic heterojunction light emitting diodes using the compound as the emitter layer. Our results indicate that, contrary to previous reports, the relative PL yield is not a good indicator of the EL quantum efficiency of a particular material. Specifically, we find that while the PL of Alq3 films is four times that of Gaq3, light emitting devices made from these two materials have comparable electroluminescence quantum efficiencies and long‐term stabilities. Furthermore, the Gaq3 devices have an approximately 50% higher power efficiency than Alq3 structures, suggesting that Gaq3 is a superior emitter material for ...

We investigate the current transport and electroluminescence mechanisms controlling the efficiency of organic heterojunction, green light emitting devices consisting of tris‐(8‐hydroxyquinoline) aluminum (Alq) and a hole transport layer (HTL). From the dependence of the current‐voltage characteristics and luminescence efficiency on layer thickness and HTL composition, we find that current is controlled by trap‐limited transport of electrons injected into Alq. Electroluminescence efficiency, on the other hand, is controlled by hole injection from the HTL into Alq. The luminescence is generated by recombination of electrons localized at a high density trap in the Alq, and holes injected from the HTL. These results provide insight into the fundamental processes which control the operating voltage and luminescence efficiency of vacuum deposited organic light emitters.

We directly observe by reflection high‐energy electron diffraction, the quasiepitaxial growth of crystalline organic quantum‐well structures grown by the ultrahigh vacuum process of organic molecular beam deposition. We show that each of four alternating layers of two organic molecules grows in a crystalline form without sufficient strain to induce amorphous growth, regardless of significant lattice mismatch which might exist between the alternating films. Our results clearly demonstrate the ability to engineer a completely new class of van der Waals‐bonded thin film materials and structures based on crystalline organic semiconductors, with applications to optoelectronics.

Excitons are integral to nearly all electronic processes in molecular organic solids. Exciton diffusion is a dominant method of energy transfer; exciton absorption dominates the absorption spectrum; and exciton formation is necessary for luminescence and photoconductivity. Indeed, tracking excitonic processes is the key to understanding the physical behavior of molecular organic semiconductors. In this chapter, we examine excitonic behavior in doped molecular organic thin films, focusing on energy-transfer processes between dissimilar organic molecules.

We quantitatively study the electric field distributions in Hg0.56Cd0.44Te avalanche photodiodes recently reported for use in the 1.6–2.5 μm wavelength region using a two‐dimensional solution of Poisson’s equation. It is found that, contrary to previous reports, there is no evidence for large uniform avalanche gain in these diodes. Furthermore, to first order, it is shown that the ionization rate ratio of electrons to holes in the diodes demonstrated to date is on the order of unity. Hence, it is not expected that the present diodes will lead to low noise operation superior to Ge or In0.53Ga0.47As/InP avalanche photodetectors.

The conduction‐band discontinuities and interface charge densities of several n‐N isotype InxGa1−xAs/InP (x≂0.53) heterojunctions with lattice mismatches (Δa/a) ranging from +0.26 to −0.24% were measured using capacitance‐voltage techniques. To facilitate these measurements, organic‐on‐inorganic contact barrier diodes were used. Extremely low interface charge densities (

We present an overview of the metal/organic—Schottky-type, and organic/organic heterojunction photovoltaic (PV) cells grown by vacuum deposition of molecular organic thin films. Recent developments leading to multilayer organic PVs are highlighted. The use of organic phosphors for enhancement of the UV response of conventional PV technologies is also discussed.

It has recently been shown that ordered, organic thin films of planar stacking molecules can be grown with monolayer uniformity and control over large substrate distances by the ultrahigh vacuum process of organic molecular beam deposition (OMBD). Due to this ability to grow films with such a high degree of order, it was demonstrated by So, et al1 , 2 that multiple quantum well stacks consisting of alternating layers of the archetype compounds, 3,4,9,10 perylenetetracarboxylic dianhydridc (PTCDA) and 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA) exhibit exciton quantum confinement That is, energy shifts in the absorption spectrum, as well as time resolved photolumincscence indicates systematic changes with layer thickness, as the thickness is reduced from 500Å to 10Å. While these early data were compelling, they opened up many questions as to the nature of excitons in closely packed organic molecular systems. Hence, in this work, we have extended this early investigation by measuring the electroabsorption, the absorption and the fluorescence spectra of organic MQW stacks consisting of PTCDA+NTCDA, as well as 3,4,9,10 peryleneietracarboxylic-bis-benzimidazole (PTCBI)+NTCDA. These new investigations provide further information essential to understanding the nature of excitons in these van der Waals-bonded molecular solids.

Summary not available.

We introduce a model to calculate the equilibrium configuration of the interface between two monolayers of large, planar organic molecules bonded by van der Waals (vdW) forces. The model significantly simplifies analysis by replacing the conventional atom-atom vdW potential summation with a single ellipsoidal potential centered in the molecular plane. Our results indicate that recent observations of crystalline «quasiepitaxial» vacuum growth of incommensurate lattices of these planar molecular films results from the relative intralayer stiffness as compared to the small interlayer shear stress. The model can be used to predict molecular structures which are likely to form quasiepitaxial layers

In previous work, we have successfully developed techniques to fabricate low-loss rib waveguides in a crystalline organic compound, namely, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA). Here, we demonstrate apparently the first optical directional coupler using an index-matching layer in similar crystalline organic semiconductor waveguides. We also observed switching of the guided light between the waveguides in the PTCDA couplers by pumping the surface of one waveguide in the coupling region with 0.514 micrometer wavelength light. A directional coupler typically consists of a pair of parallel channel waveguides with a gap between them. The gap width and the refractive index discontinuity between the guides and the gap are small enough to allow the guided light to couple from one waveguide to the other by the overlapping evanescent tails of the guided modes. However, there is a large refractive index discontinuity of 1.017 for TE modes at the interface between a PTCDA waveguide and an air gap at lambda = 1.06 micrometer. The large index discontinuity causes a small coupling coefficient and a long coupling length. The best way to increase the coupling coefficient between two rib waveguides is to fill the gap with a layer whose index is only slightly lower than the adjacent guides. In our experiments, we employed AZ 1400 photoresist as the index-matching layer material for PTCDA couplers. AZ 1400 photoresist has a relatively high index of 1.61 and low absorption at lambda = 1.06 micrometers. In this case, for a coupler having 0.5 micrometer thick, 2 micrometer wide waveguides and 1 micrometer gap, Kappa approx. - 0.50 mm-1, which is about 40 times greater than that for the coupler without an index-matching layer. Correspondingly, the coupling length is 3.14 mm.

It is well known that a key element in advanced photonic system architectures are arrays of sources and detectors. For example, such devices are useful in optoelectronic switching matrices,1 byte-wide communication, and active wavelength division multiplexing. The effective bandwidth of a system is equal to the bandwidth of a single optical channel multiplied by the total number of parallel channels. Hence, the achievement of very high frequency arrays is an important step in realizing systems which operate at terabit bandwidths and beyond.

Recently, there is an increasing interest in smart pixel arrays for use in high density, high bandwidth interconnection networks.1,2 Optoelectronic integrated circuits (OEICs) are attractive components for such arrays. There are, however, critical limitations associated with 2-D chip architectures that prevent the OEIC-based design from achieving the expected high performance. One issue is the electrical voltage supply and pixel logic control lines which must be routed to each pixel. The nonzero impedance of these interconnects introduces crosstalk which ultimately limits the bandwidth of the system. In addition, the dc bias lines and their associated ac decoupling circuitry consume valuable chip area. We propose a novel interconnection architecture to confront the issues of crosstalk and layout, which utilizes the principle of optically powered smart pixels.3 Here, optical powering is locally provided to each pixel using an integrated photovoltaic cell. In this paper, we demonstrate an optically powered, integrated smart pixel. The InP based circuit can be dynamically tuned with an optical control beam to operate as an amplifier, bistable switch or as a latch/reset. The circuit has an optoelectronic gain of 2.5–11, and operates at 80 Mbit/s with an optical switching energy of only 3.8 pJ.

Monolithically integrated InP-based optical receivers are attractive for long-wavelength high-density optical communications. Here we reported an In0.53Ga0.47As receiver which consists of an In0.53Ga0.47As PIN photodiode and an In0.53Ga0.47As JFET transimpedance amplifier. The In0.53Ga0.47As JFETs have previously demonstrated high stability and suitable for large-scale InP-based OEICs.1 A narrow-gate In0.53Ga0.47As JFET (5μm wide and 30μm long) is used as an active feedback resistor for the transimpedance amplifier. The output resistance of the narrow-gate transistor operated in its linear region can be dynamically tuned over a wide range. In addition to the active resistors, the transimpedance amplifier has a common source inverter, a level-shifter and an output buffer. Figure 1 shows the circuit diagram and photomicrograph of the monolithic receiver.

Optical powering of optoelectron integrated circuits (OEICs) significantly improves their performance in high density photonic systems as compared to conventional designs employing electrical powering of circuits.1 Here optical powering replaces the dc bias lines with integrated photovoltaic (PV) cells in each pixel. The PV cell is illuminated with an external light source (e.g. laser) and converts this optical power beam into electrical power which subsequently drives the circuitry within that pixel. The total absence of the parasitic capacitances and inductances in the optical beam reduces inter-pixel cross-talk as compared with conventional dc bias lines. This leads to significantly increased bandwidths in the optically powered case. In addition, optical powering reduces interconnection complexity associated with routing bias lines to each pixel in a high-density, two dimensional array. An optically powered interconnection system has already been demonstrated in hybrid form.2,3 In this present work, we discuss an integrated optoelectronic logic circuit in which the power and control are both provided using optical sources.

Recently, crystalline organic semiconductors have been of interest because of their excellent electronic and optical properties. One crystalline organic semiconductor, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), is of particular importance owing to its usefulness in optoelectronic integrated circuits based on PTCDA-inorganic semiconductor heterojunction structures.

Multistage networks are widely used in parallel signal-processing systems for interconnection, sorting, and computing.1 In such a network, each stage is composed of a fixed connection pattern and an array of 2 × 2 bypass/exchange switch modules. The inherent parallelism and potentially low crosstalk of optics can be fully utilized for the fixed connections at each stage. However, a light-efficient and easily controlled optical switch module is difficult to build. A more promising system uses optics for the fixed connections and optoelectronic technology for the switching.

We discuss recent results in ultrahigh efficiency electrophosphorescent organic light emitting devices. In particular, we consider electrophosphorescent devices emitting in the red, green and blue spectral regions, and the relationship between efficiency and energy transfer. Both small molecular weight and polymer OLEDs are discussed. Furthermore, very high brightness, white emitting electrophosphorescent OLEDs will be described.

We discuss the properties of organic‐on‐inorganic (OI) semiconductor contact barrier diodes. A model for charge transport is developed which suggests that thermionic emission over the organic/inorganic contact barrier dominates at low current densities, whereas space‐charge effects dominate transport through the organic layer at high current densities. The effects of charge trapping in the organic layer are also considered. This model is applied to OI diodes using thin films of the prototypical aromatic compound; 3,4,9,10‐perylenetetracarboxylic dianhydride, (PTCDA) vapor‐deposited onto n‐ and p‐Si substrates. Several electrical and optical properties of PTCDA are investigated to provide a basis for analyzing the OI diodes. Both ohmic and space‐charge‐limited transport are observed in the PTCDA. We discuss mobility, transient response, and photoresponse of the thin‐film organic material. Also described are the general properties of organic‐on‐inorganic contact barrier diodes which employ PTCDA and related...

The effects that interface traps have on the determination of the heterojunction band discontinuity energies ΔEc measured via capacitance‐voltage analysis are considered. We show that both the trap density σiK and conduction‐band discontinuity energy ΔEcK measured using the method of Kroemer, Chien, Harris, and Edwall [Appl. Phys. Lett. 36, 295 (1980)] are functions of the heterointerface width d, the difference between the actual and the measured heterojunction positions Δxj, and the doping levels of the two contacting materials. These error sources can be corrected by using simple amended equations developed in this study. This amended technique improves the measurement accuracy of both trap density and heterojunction band discontinuity energy, is easy to use, and is relatively insensitive to variations in doping and trap density in the interface region. This technique is applied to the analysis of a vapor phase epitaxial N‐n InP/In0.53 Ga0.47 As heterojunction for which we find ΔEc =(0.24±0.01) eV.

We report on low‐dark‐current IN0.53GA0.47As photodiodes in which generation‐recombination current dominates diode leakage up to as high as 100 V. At higher voltages, tunneling currents become dominant, resulting in the soft breakdown characteristic widely observed in these materials. The dark current versus voltage characteristics have been fit to variations in current of over six orders of magnitude and a temperature range greater than 150 K using a theory which includes generation‐recombination, tunneling, and shunt components.

We report experiments performed on iron particles with radii in the range 40–100 A, produced by pulsed evaporation from an electroplated tungsten filament in a cryogenic helium gas atmosphere. Flight times in electric fields of singly charged particles produced in the evaporation process yield values for gas velocity and charged particle mobility. Particle size distributions are determined both by electron microscopy and from the mobility. The latter method yields particle size distributions quickly and with good statistics, but with indicated radii larger by about 20 A than those determined by electron microscopy. The discrepancy, which is most important for the smallest particles, is attributed to the effect of van der Waals interaction between the iron particles and the gas atoms. Comparison is made with theory, which connects the van der Waals interaction with the dielectric response functions. For particles in this size range, a van der Waals interaction determined from bulk iron data gives a satisfa...

The properties of semi‐insulating (SI) Fe‐implanted InP are studied via the electrical and optical properties of p+‐SI‐n+ InP diodes. The current‐voltage‐temperature characteristics reveal a rich variety of transport processes in which the deep levels of Fe play a prominent role, including tunneling and field‐assisted thermionic emission from these levels, and space‐charge‐limited double‐injection current effects. From the analysis of these currents, different experimental estimates of the position of the deep levels have been obtained. These are compared with a direct experimental determination of their position from the measurement of the photocurrent spectra of the p+‐SI‐n+ diodes. These results establish the position of the iron acceptors at a level lying between 0.60–0.65 eV below the conduction band minimum. Capacitance spectroscopy of the p+‐SI‐n+ diodes revealed additional defect levels and carrier freeze‐out effects at low temperatures.

We report on deep levels in In0.53Ga0.47 As/InP heterostructure avalanche photodiodes grown by liquid‐phase epitaxy. Two electron levels have been identified and studied using both admittance spectroscopy and a static capacitance‐voltage technique. One level, found only in the InP layer, is acceptor‐like with an activation energy of etA = 0.20±0.02 eV and has a density in the bulk of the InP layer of NtA≊ 1015 cm−3. The density of the trap increases sharply at the In0.53Ga0.47 As/InP heterointerface to a value nearly ten times the background carrier concentration in this region. Filling of this trap at low temperatures reduces the conduction band discontinuity at the heterointerface from Δec = 0.19 to 0.03 eV due to repulsion of the bands. The second trap, which is characteristic only of the In0.53Ga0.47 As, has an activation energy of etB = 0.16±0.01 eV, and a density of between 3×1013 and 8×1013 cm−3.

We discuss a new technique for measuring the net carrier concentrations, layer thicknesses, and deep level spectra of epitaxial InP and related compounds used in photonic device applications. The technique involves the formation of an organic‐on‐inorganic (OI) semiconductor contact barrier by vacuum sublimation of the compound: 3, 4, 9, 10‐perylenetetracarboxylic dianhydride onto an inorganic semiconductor wafer. The OI barriers are reproducible from wafer to wafer, and can be as high as φBn ≊0.55 V over the entire range of InGaAs (P) compounds lattice matched to InP. High voltages (≳100 V in some cases) can be applied to the small area OI devices (as defined by an ohmic contact pad deposited on the organic film), allowing for deep depletion. Thus, high resolution carrier concentration measurements over extensive distances in all three wafer dimensions are obtained. These data are used to derive both the doping levels and layer thickness contours over the crystal surface. Finally, the OI devices can be re...