Tunnel injection and power efficiency of InGaN/GaN light-emitting diodes

The results of studying the influence of the finite tunneling transparency of injection barriers in light-emitting diodes with InGaN/GaN quantum wells on the dependences of the current, capacitance, and quantum efficiency on the p-n junction voltage and temperature are presented. It is shown that defectassisted hopping tunneling is the main transport mechanism through the space charge region (SCR) and makes it possible to lower the injection barrier. It is shown that, in the case of high hopping conductivity through the injection barrier, the tunnel-injection current into InGaN band-tail states is limited only by carrier diffusion from neutral regions and is characterized by a close-to-unity ideality factor, which provides the highest quantum and power efficiencies. An increase in the hopping conductivity through the space charge region with increasing frequency, forward bias, or temperature has a decisive effect on the capacitance-voltage characteristics and temperature dependences of the high-frequency capacitance and quantum efficiency. An increase in the density of InGaN/GaN band-tail states and in the hopping conductivity of injection barriers is necessary to provide the high-level tunnel injection and close-to-unity power efficiency of high-power light-emitting diodes.     

Deep centers and negative temperature coefficient of the breakdown voltage of SiC p-n structures

The temperature coefficient of the breakdown voltage of 6H-SiC p-n structures has been investigated. It is shown that the temperature dependence of the breakdown voltage can be explained by charge exchange on deep acceptor levels in the space charge layer. The computational results are in good agreement with the experimental data obtained for boron-doped 6H-SiC p-n structures. Fiz. Tekh. Poluprovodn. 31, 866–868 (July 1997)     

The effect of damaging radiation (<Emphasis Type="Italic">p,e, γ</Emphasis>) on photovoltaic and tunneling GaAs and GaSb <Emphasis Type="Italic">p-n</Emphasis> junctions

The properties of multiple-junction solar cells depend on the properties of the constituent photovoltaic and tunneling p-n junctions. In this study, the properties of the space-charge region for photovoltaic and tunneling p-n junctions were examined using the dark current-voltage characteristics for two semiconductors: GaSb (a narrow-gap semiconductor) and GaAs (a wide-gap semiconductor). The effects of irradiation with protons (the energy of 6.78 MeV and the maximum fluence of 3 × 10¹² cm^?2), electrons (the energy of 1 MeV and the maximum fluence of 3 × 10¹⁶ cm^?2), and γ-ray photons (the energy of 1.17–1.33 MeV and the maximum dose of 17 Mrad) on the lifetime of charge carriers in the space-charge region of photovoltaic p-n junctions and on the peak current of connecting tunneling p-n junctions were studied. The coefficients of the damage for the inverse lifetime are determined for photovoltaic p-n junctions. The coefficients of equivalence between the used types of radiation are determined; these coefficients are found to be almost independent, on the order of magnitude, of the type and material of the p-n-junction (and nearly equal for photovoltaic GaAs p-n junctions and tunneling GaAs and GaSb p-n junctions).     

Silicon LEDs with room-temperature dislocation-related luminescence, fabricated by erbium ion implantation and chemical-vapor deposition of polycrystalline silicon layers heavily doped with boron and phosphorus

Light-emitting diodes (LEDs) have been fabricated in which optically active centers are formed by implantation of erbium ions into silicon and subsequent high-temperature annealing in an oxidizing atmosphere and the p-n junction and the ohmic contact are formed by chemical vapor deposition of polycrystalline silicon layers doped with boron and phosphorus, respectively. The luminescent properties of the LEDs have been studied. Use of polycrystalline layers makes it possible to eliminate the losses in the bulk of the light-emitting Si:Er layer. These losses are inevitable if the conventional ion implantation and diffusion methods are employed. At 80 K, the variation of electroluminescence spectra in the spectral range of the dislocation-related luminescence with the drive current is well described if the spectrum is decomposed into three Gaussian components whose peak positions and widths are current-independent and amplitudes linearly increase with the current. At 300 K, a single peak is observed in the spectral range of the dislocation-related luminescence at ～1.6 μm.     

Effect of thermal annealing of radiation defects on the noise characteristics of silicon <Emphasis Type="Italic">p-n</Emphasis> structures with a thin multiplication region

Specific features of changes in the noise spectral density and the lifetime of minority charge carriers in Si p-n structures with a thin multiplication region under thermal annealing of radiation defects were studied. It is shown that the change in the frequency characteristics of noise in p-n structures is related to the recovery of surface states. A qualitative explanation of self-limitation of the avalanche process in p-n structures with a thin multiplication region is suggested.     

Radiation hardness of SiC ion detectors under relativistic protons

Schottky diodes based on 6H-SiC epitaxial films exposed to 1000 MeV protons at a dose of 3×10¹⁴ cm^?2 have been studied by precision alpha spectrometry. Parameters of deep levels introduced by protons were determined by deep-level transient spectroscopy. The number of vacancies generated in proton tracks was found using TRIM software. The width of the space charge region and the hole diffusion length before and after irradiation were obtained by processing the alpha-spectrometry and capacitance measurements. Minor variations in the charge transport properties of epitaxial 6H-SiC detectors were observed.     

Capacitance of MOS diodes on substrates doped non-uniformly near the surface

The usual assumption of uniform doping in the space charge region no longer holds if the doping near the semiconductor surface is changed appreciably by thermal oxidation and/or ion implantation. Poisson's equation becomes the non-linear, but can be solved using suitable approximations for the dependence on the voltage. Thus the exact form of the doping profile is taken into account.The C?V curves of MOS diodes differ considerably from those for uniform doping due to the altered relation between the surface potential and the total charge of the semiconductors as well as due to the altered width of the space charge region. These two contributions are reduced to additive terms if the space charge region covers completely the region with altered doping.For weak depletion the slope of the C?V curves is larger for pile-down of acceptors and pile-up of donors in p-type silicon. The slope becomes smaller for increasing depletion, because the space charge region spreads now to more heavily doped regions of the semiconductor. For pile-up of donors and pile-down of acceptors in n-type silicon, the curves are initially less declined and become steeper according to the smaller doping in the bulk of the semiconductor.     

High-voltage (900 V) 4 <Emphasis Type="Italic">H</Emphasis>-SiC Schottky diodes with a boron-implanted guard <Emphasis Type="Italic">p-n</Emphasis> junction

High-voltage (900 V) 4H-SiC Schottky diodes terminated with a guard p-n junction were fabricated and studied. The guard p-n junction was formed by room-temperature boron implantation with subsequent high-temperature annealing. Due to transient enhanced boron diffusion during annealing, the depth of the guard p-n junction was equal to about 1.7 μm, which is larger by approximately 1 μm than the projected range of 11 B ions in 4H-SiC. The maximum reverse voltage of fabricated 4H-SiC Schottky diodes is found to be limited by avalanche breakdown of the planar p-n junction; the value of the breakdown voltage (910 V) is close to theoretical estimate in the case of the impurity concentration N = 2.5 × 10¹⁵ cm^?3 in the n-type layer, thickness of the n-type layer d = 12.5 μm, and depth of the p-n junction r _j = 1.7 μm. The on-state diode resistance (3.7 mΩ cm²) is controlled by the resistance of the epitaxial n-type layer. The recovery charge of about 1.3 nC is equal to the charge of majority charge carriers that are swept out of an epitaxial n-type layer under the effect of a reverse voltage.     

The role of radiation damage on the current-voltage characteristics of p-n junctions

The effects of radiation damage on the current-voltage characteristics of silicon p-n diodes are studied. Radiation damage is introduced by the implantation of carbon ions into the depletion region of the device. The physical properties of the damage centres are examined by means of thermally stimulated current (T. S. C.) measurements, and by the measurement of the temperature dependence of the reverse leakage. The results at low implantation doses are explained by means of a single level Shockley-Read-Hall model, while at higher doses charge compensation effects are introduced. Capacitance-voltage measurements are used as a means of verifying these conclusions, and further useful data is obtained from the results of low temperature annealing experiments.     

Voltage dependence of the differential capacitance of a p +-n junction

The dependences of the differential capacitance and current of a p ⁺-n junction with a uniformly doped n region on the voltage in the junction region are calculated. The p ⁺-n junction capacitance controls the charge change in the junction region taking into account a change in the electric field of the quasi-neutral n region and a change in its bipolar drift mobility with increasing excess charge-carrier concentration. It is shown that the change in the sign of the p ⁺-n junction capacitance with increasing injection level is caused by a decrease in the bipolar drift mobility as the electron-hole pair concentration in the n region increases. It is shown that the p ⁺-n junction capacitance decreases with increasing reverse voltage and tends to a constant positive value.     

Dependence of GaN photoluminescence on the excitation intensity

The dependence of the edge photoluminescence (PL) intensity on the excitation intensity in (0001) HVPE-grown GaN samples has been studied. The specific behavior found is that, at a low excitation level, the dependence is markedly superlinear, namely, superquadratic, and at high excitation levels it is nearly linear. A model accounting for the observed superquadratic behavior is proposed which is based on the identity of the recombination processes in the surface space charge region (SCR) under optical excitation with those in the SCR of the Schottky barrier or a p-n junction under current flow conditions. The superquadratic dependence is obtained analytically under the assumption that the nonradiative recombination channel is associated with multiple-hopping tunneling along a dislocation, which is formed by a chain of carrier localization centers and crosses the SCR. The experimental dependence of the PL intensity on the excitation intensity is a power-law function. The distance between the neighboring localization centers, i.e., the period of the potential along the dislocation, is determined as ～4.1 nm.     

Effect of the annealing temperature on erbium ion electroluminescence in Si:(Er,O) diodes with (111) substrate orientation

The influence of the temperature of secondary annealing, stimulating the formation of optically and electrically active centers, on the erbium ion electroluminescence (EL) at λ≈1.54 μm in (111) Si:(Er,O) diodes has been studied. The diodes were fabricated by the implantation of 2.0 and 1.6 MeV erbium ions at doses of 3×10¹⁴ cm⁻² and oxygen ions (0.28 and 0.22 MeV, 3×10¹⁵ cm⁻²). At room temperature, the EL intensity in the breakdown mode grows with the annealing temperature increasing from 700 to 950°C. At annealing temperatures of 975–1100°C, no erbium EL is observed in the breakdown mode owing to the formation of microplasmas. The intensity of the injection EL at 80 K decreases with the annealing temperature increasing from 700 to 1100°C. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 10, 2001, pp. 1224–1227. Original Russian Text Copyright ? 2001 by Sobolev, Emel’yanov, Nikolaev.     

Photosensitivity of In-SiO2-Cd0.28Hg0.72Te structures with a nontransparent field electrode

The photoeffect in a metal-insulator-semiconductor (MIS) structure that incorporated a Cd_0.28Hg_0.72Te compound, a low-temperature pyrolitic SiO₂, and an In layer with a thickness of 500 nm and an area of 0.5×0.5 mm² was studied. For a MIS structure with a nontransparent field electrode, the observed photoeffect consists in variation in the capacitance and high-frequency electrical conductivity of the MIS structure; this photoeffect is caused by photocarriers that are formed outside the MIS structure and reach this structure either due to diffusion or along the surface channel. This happens if the MIS structure is in the state of inversion; in this case, an eddy electric current formed crosses the induced p-n junction and closes on itself at the MIS structure periphery. It is assumed that this current and the extra voltage across the p-n junction are related by the Shockley formula. The following parameters were evaluated: the coefficient β in the Shockley formula (β characterizes the nonideality of the p-n junction); the product R ₀ A of the resistance for zero bias by the area of the p-n junction; and the surface area ΔS of collection of the charge carriers. It was found that β=1.52, R ₀ A=2.7×10⁵ Ω cm², and ΔS corresponds to a stripe that goes along the MIS-structure perimeter and has a width of 15 μm. The MIS structure studied is considered as a photodetector. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 7, 2000, pp. 822–826. Original Russian Text Copyright ? 2000 by Ovsyuk, Vasil’ev, Mashukov.     

Extension of the frequency range of the noise spectral density in silicon p-n structures irradiated with gamma-ray quanta

The possibility of intentionally shifting the high-frequency edge of plateau in the noise spectral density of silicon p-n structures to higher frequencies under irradiation with gamma-ray quanta was studied. The largest increase in the extent of the operating-frequency range was observed to amount to 2–2.5 times. As the irradiation dose increased further, the plateau width did not increase, and its boundary became less abrupt. Correlation between the variation in the effective lifetime of minority charge carriers and the width of low-frequency plateau in the noise spectral density was found. A qualitative model describing the variation in the noise spectral density with increasing irradiation dose for silicon p-n structures with microplasma channels governed by the p-n junction dimensions is suggested.     

High-voltage (1800 V) planar 4<Emphasis Type="Italic">H</Emphasis>-SiC <Emphasis Type="Italic">p-n</Emphasis> junctions with floating guard rings

Planar 4H-SiC p-n junctions with floating guard rings have been fabricated. The main junction and the rings were formed by room temperature boron implantation followed by high temperature annealing. The breakdown voltage of the p-n junctions is 1800 V, which twice exceeds that of similar junctions without guard rings and reaches 72% of the calculated breakdown voltage of a plane-parallel p-n junction with the same epitaxial layer parameters     

A discrete element small-signal equivalent circuit for forward-biased p+n diodes containing deep levels

A discrete element small-signal equivalent circuit model for p-n diodes containing deep defect levels is developed, by extending an existing model for undamaged devices. With the aid of a simple analytical expression which accurately describes the forward bias d.c. current, the enhanced small-signal conductance due to carrier recombination in the depletion region is included in the model. The influence of trapped charge on the space charge capacitance is incorporated using a simplified version of the analysis of Beguwala and Crowell. The predictions of the model are verified by experimental data from silicon p⁺n diodes, in which deep levels have been induced by electron irradiation. It is shown that the deep level activation energies may be estimated from the forward bias capacitance-voltage characteristics, yielding values which agree well with those obtained by established techniques.     

Generation-recombination and diffusion currents in HgMnTe n +-p junctions

Special features of the distributions of the space charge, the electric-field strength, and potential in the p-n junction in the narrow-gap HgMnTe semiconductor were considered using the Poisson equation. It is shown that, as the band gap narrows, the effect of free charge carriers induces the coordinate dependence of electric-field strength to deviate from the linear dependence and that of the potential to deviate from the quadratic dependence. As a result of this, and also because of an appreciable increase in the diffusion potential in the n ⁺-p junction with the degenerate n ⁺ region, the mechanisms of the charge transport become peculiar: the voltage dependence of the recombination current deviates from those following from the conventionally used analytical expressions, whereas for higher bias voltages, the diffusion current of holes from the lightly doped p region into the n ⁺ region is prevalent.     

Light emitting diodes for the spectral range λ=3.3–4.3 µm fabricated from InGaAs and InAsSbP solid solutions: Electroluminescence in the temperature range of 20–180°C (Part 2)

Light-emitting diodes (LEDs) based on p-n homo-and heterostructures with InAsSb(P) and InGaAs active layers have been designed and studied. An emission power of 0.2 (λ=4.3 µm) to 1.33 mW (λ=3.3 µm) and a conversion efficiency of 30 (InAsSbP, λ=4.3 µm) to 340 mW/(A cm²) (InAsSb/InAsSbP double heterostructure (DH), λ=4.0 µm) have been achieved. The conversion efficiency decreases with increasing current, mainly owing to the Joule heating of the p-n homojunctions. In DH LEDs, the fact that the output power tends to a constant value with increasing current is not associated with active region heating. On raising the temperature from 20 to 180°C, the emission power of the (λ=3.3 and 4.3 µm) LEDs decreases, respectively, 7-and 14-fold, to become 50 (at 1.5 A) and 7 µW (at 3 A) at 180°C.     

Special features of generation-recombination processes in the p-n junctions based on HgMnTe

New experimental data on the charge transport in p-n junctions based on Hg_1?x Mn_xTe (x≈0.11) are reported. The experimental I-V characteristics are interpreted in terms of the Sah-Noyce-Shockley theory with allowance made for special features of recombination of the charge carriers in a narrow-gap semiconductor.