Photoeffect on diffused P-N junctions with integral field gradients

A detailed analysis of a diffused junction photodiode is presented in which the illumination, monochromatic or broad-band, is applied to the diffused face. The electric field produced by the impurity distribution, assumed exponential, assists the transport and collection of minority carriers created by photons absorbed in the graded region. The theoretical study covers both the steady-state and the transient response, and takes into account the effect of surface recombination velocity. The presence of the built-in field increases the photocurrent and reduces the dark current compared with homogeneous base diodes. For p-n silicon photodiodes with 5-micron base widths and acceptor concentrations of say, 2 × 10¹⁸atoms/cm³at the surface, photosensitivities of approaching 0.01 ampere per lumen may be achieved. The transient-response analysis considers the extrinsic delay imposed by the time constant of the junction capacitance and the load resistance, and also the inherent delay caused by the transit time of the minority carriers. With moderate or high load resistances, the extrinsic delay is much larger than the transit-time delay. However, for comparable graded- and homogeneous-base photodiodes, the capacitances of graded junctions are lower, and therefore the transient response is improved on this account. The graded junctions also are shown to have greatly reduced transit-time delays because of the built-in field effect.     

Low leakage current GaAs diodes

Diodes were formed by Mg ion implantation into n-epitaxial GaAs layers on n⁺Substrates. Deep level transient spectroscopy (DLTS) measurements gave trap densities around 10¹²cm^-3in the epilayers. The reverse-biased junction currents were in the low-to-mid 10^-9A/cm²range at 10-V bias and the diodes had breakdown voltages as high as 250 V.     

The performance of IMPATT diodes under the influence of high-intensity gamma and neutron radiation

IMPATT diodes were tested under the influence of up to 1.5 × 10⁷R/h gamma radiation and 3 × 10¹²N/cm²/s fast neutrons. Major changes were noted in power output, frequency spectrum, and current-voltage characteristics. Permanent damage and total failure resulted from this test.     

Experimental determination of electron drift velocity in 4H-SiC p+-n-n+ avalanche diodes

4H-SiC p⁺-n-n⁺ diodes of low series resistivity (<1×10^-4 Ω·cm²) were fabricated and packaged. The diodes exhibited homogeneous avalanche breakdown at voltages U_b=250-270 V according to the doping level of the n layer. The temperature coefficient of the breakdown voltage was measured to be 2.6×10^-4 k^-1 in the temperature range 300 to 573 K. These diodes were capable of dissipating a pulsed power density of 3.7 MW/cm² under avalanche current conditions. The transient thermal resistance of the diode was measured to be 0.6 K/W for a 100-ns pulse width, An experimental determination of the electron saturated drift velocity along the c-axis in 4H-SIC was performed for the first time, It was estimated to be 0.8×10⁷ cm/s at room temperature and 0.75×10⁷ cm/s at approximately 360 K     

Reliability of MINP compared to MIS, SIS, and N/P silicon solar cells under 1.0-MeV electron and environmental effects

The effects of 1.0-MeV electron radiation are compared for MIS, SIS, N/P, and MINP silicon solar cells. MIS, SIS, and N/P silicon solar cells are comparable in performance except that SIS cells degraded faster due to use of n-type Si substrates. MINP cells exhibited superior performance in that efficiency degraded 9 percent at a fluence of 1 × 10¹⁵e^-/cm²and 32 percent at a fluence of 1 × 10¹⁶e^-/cm²compared to 29 percent and 49 percent, respectively, for N/P cells. MINP cells utilize an SiO2insulator layer over a thin N-region, and a low work function metal contact. This design gives a high ultraviolet response and low surface recombination velocity which maintains high efficiency since most of the radiation loss occurs in the infrared region due to bulk damage effects.     

Demonstration of an SiC neutron detector for high-radiationenvironments

Neutron response studies have been performed on Schottky diodes fabricated using 4H-SiC material. These studies indicate that neutron detection using SiC diodes is possible without significant degradation in the energy resolution, noise characteristics or, most importantly, the neutron counting rate even after exposure to neutron fluences of 3.4×10¹⁷ n_th/cm² (1×10¹⁷ n_fast/cm²; E_n.fast >1 MeV), the highest yet examined. The results represent orders of magnitude increased device lifetime in neutron fields compared to commercial silicon based detectors. Additionally, detector response was found to be linear up to thermal neutron fluxes of 2000 n_th/cm²/s. However, degradation in the charge collection efficiency due to neutron damage-induced defects prevented self-biased operation after exposures above ~5.7×10¹⁶ n _th/cm². A carrier removal rate of 9.7±0.7 cm^-1 was calculated from C-V doping profile measurements on neutron irradiated samples. These results demonstrate the viability of SiC-based detectors for a variety of radiation monitoring applications     

Low-temperature fabrication of p+-n diodes with300-Å junction depth

Gas immersion laser doping (GILD) was used to fabricate p⁺ -n diodes with 300-Å junction depth. These diodes exhibit ideality factors of 1.01-1.05 over seven decades of current, reverse leakage current densities ⩽10 nA/cm² at -5-V reverse bias, breakdown voltages above 100 V, and electrical activation of the boron impurity to concentrations approaching 1×10²¹ atoms/cm³. This behavior is achieved without the use of a furnace or rapid thermal anneal     

Characterization of reverse leakage components for ultrashallowp+/n diodes fabricated using gas immersion laser doping

In this letter we report on fabrication of p⁺/n diodes with junction depths less than 60 nm using gas immersion laser doping (GILD). Statistics for diodes with junction depths of 39 nm and 50 nm, surface concentrations exceeding 10²⁰ atoms/cm³, and sheet resistances less than 160 Ω/□ are presented. Values for area, perimeter, and corner leakage currents are measured at less than 1.6 nA/cm², 2.5 fA/μm and 10 fA/corner respectively, at 3.4 V reverse bias. These characteristics demonstrate that the laser doping process is viable for source/drain doping in 0.18 μm CMOS technology     

Injection electroluminescence in metal-semiconductor tunnel diodes

Injection electroluminescence has been studied in metal-semiconductor (MS) and in metal-insulator-semiconductor (MIS) tunnel diodes. The diodes were fabricated from degenerately doped p-type ZnTe. Bandgap recombination radiation has been observed at 293°K, 77°K and 4°K. The linewidth narrows from approximately 120 Å at 293°K to approximately 60 Å at temperatures below 77°K. External efficiencies of 10⁻⁴ to 10⁻⁶ have been observed. For current densities below 10³ A/cm² the light output increases as the fourth or fifth power of the current density. For current densities greater than 10³ A/cm² the light varies linearly or slightly sublinearly with current density. A new model for the emission from MS tunnel diodes is proposed which accounts for the observation that light emission occurs when the semiconductor is negatively biased. No evidence of stimulated emission has been observed up to current densities of 10⁴ A/cm².     

In-situ low energy BF2+ion doping for silicon molecular beam epitaxy

An experimental study of the p-type ion dopant BF2+ in silicon molecular beam epitaxy (MBE) is described. BF2+ was used to dope MBE layers during growth to levels ranging from 1 × 10¹⁶/cm³to 4 × 10¹⁸/cm³over a growth temperature range of 650°C to 1000°C. The layers were evaluated using spreading resistance, chemical etching, and secondary ion mass spectroscopy. Complete dopant activation was observed for all growth temperatures. Remnant fluorine in the epitaxial layer was less than 2 × 10¹⁶/cm³in all cases. Diffused p-n junction diodes fabricated in BF2+-doped epitaxial material showed hard reverse breakdown characteristics.     

Temperature Dependence of High Frequency and Noise Performance of Sb-Heterostructure Millimeter-Wave Detectors

The temperature dependence of the microwave and noise performance of zero-bias Sb-heterostructure backward diodes for millimeter-wave detection have been investigated experimentally. Both the junction capacitance and junction resistance were found to decrease with decreasing temperature, while the intrinsic cutoff frequency and sensitivity are observed to increase as the temperature is lowered. A simple physical model that captures these effects is described. The directly measured voltage sensitivity at 50 GHz for a 2times2 mum ² device increased from 3650 V/W at room temperature to 7190 V/W at 4.2 K. The measured noise equivalent power (NEP) decreased from 4.2 to 0.2 pW/Hz^1/2 as the temperature was lowered from 298 K to 4.2 K when driven from a 50- Omega source. Based on the measured RF sensitivity, S-parameters, and noise spectrum, a NEP of 0.3 pW/Hz^1/2 is projected for room-temperature operation at zero bias using a conjugately matched RF source     

The potential of diamond and SiC electronic devices for microwaveand millimeter-wave power applications

The potential of SiC and diamond for producing microwave and millimeter-wave electronic devices is reviewed. It is shown that both of these materials possess characteristics that may permit RF electronic devices with performance similar to or greater than what is available from devices fabricated from the commonly used semiconductors, Si, GaAs, and InP. Theoretical calculations of the RF performance potential of several candidate high-frequency device structures are presented: the metal semiconductor field-effect transistor (MESFET), the impact avalanche transit-time (IMPATT) diode, and the bipolar junction transistor (BJT). Diamond MESFETs are capable of producing over 200 W of X-band power as compared to about 8 W for GaAs MESFETs. Devices fabricated from SiC should perform between these limits. Diamond and SiC IMPATT diodes also are capable of producing improved RF power compared to Si, GaAs, and InP devices at microwave frequencies. RF performance degrades with frequency and only marginal improvements are indicated at millimeter-wave frequencies. Bipolar transistors fabricated from wide bandgap material probably offer improved RF performance only at UHF and low microwave frequencies     

Radiation-hardened silicon-on-insulator junction field-effect transistors fabricated by a self-aligned process

A self-aligned process has been developed for fabricating JFET's in zone-melting-recrystallized (ZMR) Si films on SiO2-coated Si substrates. This process has been used to fabricate n-JFET's exhibiting transconductance values up to 63 mS/mm. For 228 devices within an area of about 4 × 4 cm², the mean threshold voltage is 578 mV and the standard deviation is 22 mV. With a -15-V bias applied to the Si substrate during irradiation and device operation, the devices show low threshold voltage shift (< -75 mV) and small transconductance degradation (∼30 percent) for exposure to total-dose radiation of 10⁸rad(Si).     

Radiation-hardened silicon-on-insulator complementary junction field-effect transistors

The effects of total-dose radiation have been investigated for complementary junction field-effect transistors fabricated in zone-melting recrystallized Si films on SiO2-coated Si substrates. With a - 5-V bias applied to the Si substrate during irradiation and device operation, both n- and p-channel devices show low threshold-voltage shift (<-0.09 and <-0.12 V, respectively), low leakage currents (<- 1- and <3-pA/µm channel width, respectively) and small transconductance degradation (<15 percent) for total doses up to 10⁸rad (Si).     

Pulsed ionizing radiation recovery characteristics of MSI GaAs integrated circuits

GaAs Schottky Diode FET Logic Divide-by 8 circuits have been characterized for transient response when exposed to 20 ns FXR pulses at 25°C. A logic upset threshold of about 10⁸rad/s was observed. At dose rates of 2 × 10¹⁰rads/s, functional operation was restored in 5 µs. A discussion of logic upset mechanisms is presented, attempting to explain both short and long term recovery observations.     

Electrical properties of Ga-implanted Si p+-n shallowjunctions fabricated by low-temperature rapid thermal annealing

p⁺-n shallow-junction diodes were fabricated using on-axis Ga⁶⁹ implantation into crystalline and preamorphized Si, at energies of 25-75 keV for a dose of 1×10¹⁵/cm ², which is in excess of the dosage (2×10¹⁴/cm²) required to render the implanted layer amorphous. Rapid thermal annealing at 550-600°C for 30 s resulted in the solid-phase epitaxial (SPE) regrowth of the implanted region accompanied by high Ga activation and shallow junction (60-130 nm) formation. Good diode electrical characteristics for the Ga implantation into crystalline Si were obtained; leakage current density of 1-1.5 nA/cm² and ideality factor of 1.01-1.03. Ga implantation into preamorphized Si resulted in a two to three times decrease in sheet resistance, but a leakage current density orders of magnitude higher     

Reduction in minority carrier storage effect by fluorine ion implantation damage

Damage is produced in p-n diodes by fluorine ion implantation to reduce minority carrier storage effect. The switching time, reverse leakage current, andI-Vcharacteristics were investigated for annealing temperature between 450°C and 650°C. The accelation energy is 130 keV and doses are 10¹³-10¹⁵/cm². Annealing causes restoration in switching time, but leakage current increases with annealing temperature rise for doses more than 1 × 10¹⁴/cm². The best diodes indicate 1.5-order reduction in switching time and 10 nA in reverse leakage current. These properties, caused by implantation damage, are retained after long-cycle annealing at 450°C and are expected to be stable under practical use. These diodes can be obtained by annealing at 450°C and they furnish satisfactory diode performance.     

Computer simulation of LSA oscillators with high doping to frequency ratios

Computer simulations of twice oversized n-GaAs diodes with random doping fluctuations operated in a transmission line (multiresonant) circuit are presented. LSA operation in this multiresonant circuit, which provides an RF square wave voltage across the diode, has been obtained for n/f ratios as high as 1 × 10⁶s/cm³.     

Steady-state and transient forward current-voltage characteristicsof 4H-silicon carbide 5.5 kV diodes at high and superhigh currentdensities

Steady-state and transient forward current-voltage I-V characteristics have been measured in 5.5 kV p⁺-n-n⁺ 4H-SiC rectifier diodes up to a current density j≈5.5×10 ⁴ A/cm². The steady-state data are compared with calculations in the framework of a model, in which the emitter injection coefficient decreases with increasing current density. To compare correctly the experimental and theoretical results, the lifetime of minority carriers for high injection level, τ_ph, has been estimated from transient characteristics. At low injection level, the hole diffusion length L_pl has been measured by photoresponse technique. For a low-doped n-base, the hole diffusion lengths are L_pl≈2 μm and L_ph≈6-10 μm at low and high injection levels respectively. Hole lifetimes for low and high injection levels are τ_pl≈15 ns and τ_ph≈140-400 ns. The calculated and experimental results agree well within the wide range of current densities 10 A/cm ²3 A/cm². At j>5 kA/cm², the experimental values of residual voltage drop V is lower than the calculated ones. In the range of current densities 5×10³ A/cm²4 A/cm², the minimal value of differential resistance R_d =dV/dj is 1.5×10^-4 Ω cm². At j>25 kA/cm², R_d increases with increasing current density manifesting the contribution of other nonlinear mechanisms to the formation steady-state current-voltage characteristic. The possible role of Auger recombination is also discussed     

A current-controlled negative-resistance effect in indium antimonide

A thin wafer of P-InSb exhibits a current-controlled negative resistance between nonsymmetrical ohmic contacts on opposite sides of the wafer. The small contact on one side of the wafer is made positive relative to the large contact on the other side. Most effective samples had small contact diameters one to four times the slab thickness. The negative resistance was present up to a temperature of 210°K for material having 2.5 × 10¹⁴/cm³acceptor concentration at 77°K. A magnetic field perpendicular to the current flow direction reduced the value of the maximum negative resistance and extended the range of bias current yielding negative resistance. Samples under 0.005 inch thick yielded negative resistance when operated continuously, for the doping of 2.5 × 10¹⁴/cm³, but thicker samples yielded negative resistance only in lower duty cycle operation. Microwave radiation lines presumably at harmonics of oscillation in the bias circuit were measured. Finally, a proposed mechanism, dependent on impact ionization, is used to predict operation to a transit-time limited frequency of, say, 8000 Mc/s for a sample whose thickness is 0.0025 inch.