Modeling ion implantation of HgCdTe

Ion implantation of boron is used to create n on p photodiodes in vacancy-doped mercury cadmium telluride (MC.T). The junction is formed by Hg interstitials from the implant damage region diffusing into the MC.T and annihilating Hg vacancies. The resultant doping profile is n⁺/n^-/p, where the n⁺ region is near the surface and roughly coincides with the implant damage, the n^- region is where Hg vacancies have been annihilated revealing a residual grown-in donor, and the p region remains doped by Hg vacancy double acceptors. We have recently developed a new process modeling tool for simulating junction formation in MC.T by ion implantation. The interstitial source in the damage region is represented by stored interstitials whose distribution depends on the implant dose. These interstitials are released into the bulk at a constant, user defined rate. Once released, they diffuse away from the damage region and annihilate any Hg vacancies they encounter. In this paper, we present results of simulations using this tool and show how it can be used to quantitatively analyze the effects of variations in processing conditions, including implant dose, annealing temperature, and doping background.     

Electrical and Optical Properties of Stacking Faults in 4H-SiC Devices

By using electron-beam-induced current (EBIC) and cathodoluminescence (CL) techniques, we characterized the electrical and optical properties of stacking faults (SFs) in 4H-SiC p ⁺/−n junctions and compared with those in Schottky diodes. In the EBIC images, SFs penetrating the p ⁺/−n junction are bright in the n ⁻ region and dark in the p ⁺ region, while SFs observed in the Schottky diode are only bright. In CL measurements, a characteristic peak (417 nm) appears at SFs in the n ⁻ region, similar to those observed in Schottky diodes. The 417-nm peak, however, does not occur obviously at either the p ⁺ layer or within the depletion region. The reason for the absence of this emission is discussed in terms of band bending at the junction.     

Dynamic minority-carrier storage in TRAPATT diodes

The occurrence of a dynamic storage of minority carriers in the highly-doped boundary regions of a TRAPATT diode and the subsequent release of these carriers into the diode's depletion region is verified for the first time in detailed computer simulations of the diode's internal dynamics. The simulations were carried out by numerical solution of the carrier transport equations in a p⁺?n?n⁺ silicon diode having a deep-diffused doping profile typical of experimental devices. The results show that it is this storage process, and not thermal generation, that controls the carrier avalanche even in very gradually graded structures. The dynamics of this phenomenon are described in detail and the implications of the results on TRAPATT oscillator performance are discussed.     

Theory of VHF detection and frequency multiplication with space-charge-limited current (SCLC) silicon diodes

A non-linear theory of transit-time effects upon VHF detection and frequency multiplication with SCLC silicon diodes, is put forward. Diffusion is neglected and carrier mobility is assumed to be field-independent. The theory applies to the SCLC resistor (n⁺νn⁺ structure) and the punch-through diode (n⁺πn⁺). An analytical theory for relatively small signal-amplitudes is developed. Then, computer calculations yield the frequency and bias dependence of the detected current and the second-harmonic amplitude.It is shown that by properly biasing the n⁺νn⁺ device (the transition region between the ohmic and square-law regions), the detected current is almost frequency-independent up to extremely high frequencies. On the other hand, the transit-time effects upon the detection characteristics of the punch-through diode are by far more important and limit the device usefulness to frequencies below the transit-time frequency. The amplitude of the second harmonic strongly depends upon frequency for both n⁺νn⁺ and n⁺πn⁺ structures.     

Numerical analysis of a double avalanche region IMPATT diode on the basis of nonlinear model

The analysis of the n⁺pvnp⁺ avalanche diode structure has been realized on the basis of the nonlinear model. This type of the diode that was named as double avalanche region (DAR) IMPATT diode includes two avalanche regions inside the diode. The phase delay which was produced by means of the two avalanche regions and the drift region v is sufficient to obtain the negative resistance for the wide frequency band. The numerical model that is used for the analysis of the various diode structures includes all principal features of the physical phenomena inside the semiconductor structure. The admittance characteristics of the DAR diode were analyzed in very wide frequency band. The obtained results contradict to the before performed analysis on basis of the approximate models and show that only diode with a sufficiently short drift region can produce active power in some frequency bands.     

Effects of time dependence of multiplication process on avalanche noise

Theoretical and experimental studies of noise generated due to the randomness of the multiplication process in the avalanche region of a uniform diode are presented. The theory extends the results of McIntyre to include the time dependence of the multiplication process. It also shows the correspondence between the results of McIntyre, Gummel and Blue, Hines and Tager. The space-charge feedback and transit-time effects have been neglected in this analysis. The theoretical and the experimental results described have shown that even at frequencies well below transit-time frequency, the importance of the factor resulting from consideration of the time dependence of the multiplication process cannot be ignored.The measurements of the avalanche noise on uniform p⁺-n-n⁺ silicon diodes are found to be in good agreement with the theory presented here.     

Effect of ultrasonic treatment on deformation effects and the structure of local centers in the substrate and in the contact regions of M/n−n +-GaAs structures (M=Pt, Cr, W)

The effect of ultrasonic treatment on the physicochemical, structural, and electrical properties of Pt, Cr, W/n-n ⁺-GaAs structures has been studied. It is shown that the ultrasonic treatment produces spatial and chemical ordering of the contact GaAs region. This decreases the reverse currents in diode structures with a Schottky barrier. A possible mechanism of the effect of ultrasonic treatment on the structural and chemical reorganization in a M/n-n ⁺-GaAs contact is discussed. Fiz. Tekh. Poluprovodn. 31, 503–508 (April 1997)     

Operation of a semiconductor opening switch at ultrahigh current densities

The operation of a semiconductor opening switch (SOS diode) at cutoff current densities of tens of kA/cm² is studied. In experiments, the maximum reverse current density reached 43 kA/cm² for ∼40 ns. Experimental data on SOS diodes with a p ⁺-p-n-n ⁺ structure and a p-n junction depth from 145 to 180 μm are presented. The dynamics of electron-hole plasma in the diode at pumping and current cutoff stages is studied by numerical simulation methods. It is shown that current cutoff is associated with the formation of an electric field region in a thin (∼45 μm) layer of the structure’s heavily doped p-region, in which the acceptor concentration exceeds 10¹⁶ cm⁻³, and the current cutoff process depends weakly on the p-n junction depth.     

Frequency characteristics of diodes with intervalley electron transfer that are based on variband In x ( z )Ga1 ? x ( z )As with various cathode contacts

A two-level model of intervalley electron transfer in a variband semiconductor is used to study the operation of a Gunn diode based on variband In _x(z)Ga_{1 − x(z)}As with n ⁺-n cathodes and n ⁺-n ⁻-n cathodes for different lengths of the active region and different thicknesses of the variband layer. It is demonstrated that the critical frequency of a GaAs-In_0.4Ga_0.6As diode (280–290 GHz) is higher than the critical generation frequencies of GaAs, In_0.4Ga_0.6As, and In_0.2Ga_0.8As diodes. Original Russian Text ? I.P. Storozhenko, 2007, published in Radiotekhnika i Elektronika, 2007, Vol. 52, No. 10, pp. 1253–1259.     

Avalanche Mechanism in p +-n −-n + and p +-n Mid-Wavelength Infrared Hg1−x Cd x Te Diodes on Si Substrates

Hg_1−x Cd _x Te mid-wavelength infrared (MWIR) p ⁺-n ⁻-n ⁺ and p ⁺-n ⁻ avalanche photodiodes (APDs) with a cut-off of 4.9 μm at 80 K were fabricated on Si substrates. Diode characteristics, avalanche characteristics, and excess noise characteristics were measured on two devices. Temperature-dependent diode and avalanche characterization was performed. Maximum 3 × 10⁶ Ω cm² and 9 × 10⁵ Ω cm² zero-bias resistance times active area (R ₀ A) products were measured for the p ⁺-n ⁻-n and p ⁺-n devices at 77 K, respectively. Multiplication gains of 1250 and 410 were measured at −10 and −4 V for the p ⁺-n ⁻-n ⁺ and p ⁺-n APDs at 77 K, respectively, in the front-illumination mode with the help of a laser with an incident wavelength of 632 nm. The gains reduce to 200 and 50 at 120 K, respectively. The excess noise factor in all APDs was measured to be in the range of 1 to 1.2.     

Edge electroluminescence in small-area silicon p +-n diodes heavily doped with boron: Analysis of model representations

The experimental results and model representations of the edge electroluminescence of two published studies for small-area silicon p ⁺-n diodes heavily doped with boron are analyzed. In one of these studies it was assumed that edge electroluminescence appears in the p ⁺ region of the diode, and in the other, in the n region of the diode. In the latter case, it was demonstrated that electroluminescence indeed arose in the n region and was caused predominantly by the radiative recombination of free excitons. It is shown that similar model concepts are also applicable to the other study. Based on several independent experimental studies (of edge photoluminescence, electroluminescence, and radiation absorption by free carriers), it is demonstrated that the linear or close-to-linear dependences of the edge-luminescence intensity on the excitation intensity, observed in single-crystal silicon at high injection levels, are caused by the close-to-linear dependences of the exciton concentration on the free-carrier concentration. The results of this study extend the capability of luminescence methods for determining the carrier lifetimes to the region of high injection levels.     

p+-n--n+-type power diode with crystalline/nanocrystalline Si mosaic electrodes

Using p⁺-type crystalline Si with n⁺-type nanocrystalline Si (nc-Si) and n⁺-type crystalline Si with p⁺-type nc-Si mosaic structures as electrodes, a type of power diode was prepared with epitaxial technique and plasma-enhanced chemical vapor deposition (PECVD) method. Firstly, the basic p⁺-n^--n⁺-type Si diode was fabricated by epitaxially growing p⁺- and n⁺-type layers on two sides of a lightly doped n^--type Si wafer respectively. Secondly, heavily phosphorus-doped Si film was deposited with PECVD on the lithography mask etched p⁺-type Si side of the basic device to form a component with mosaic anode. Thirdly, heavily boron-doped Si film was deposited on the etched n⁺-type Si side of the second device to form a diode with mosaic anode and mosaic cathode. The images of high resolution transmission electronic microscope and patterns of X-ray diffraction reveal nanocrystallization in the phosphorus- and boron-deposited films. Electrical measurements such as capacitance-voltage relation, current-voltage feature and reverse recovery waveform were carried out to clarify the performance of prepared devices. The important roles of (n^-)Si/(p⁺)nc-Si and (n^-)Si/(n⁺)nc-Si junctions in the static and dynamic conduction processes in operating diodes were investigated. The performance of mosaic devices was compared to that of a basic one.     

Laser beam induced current imaging of reactive ion etching induced n-type doping in HgCdTe

The nondestructive optical characterization technique of laser beam induced current (LBIC) has been used to illustrate the effects of reactive ion etching (RIE) of mid-wavelength infrared n-type HgCdTe. RIE may be used as a method of n-p junction formation, as a means of forming n⁺ ohmic contacts to wider bandgap HgCdTe, or for mesa isolation etching of epilayers for HgCdTe detectors and emitters. Along with experimental measurements of the LBIC phenomena, this paper introduces the simulation of LBIC signals using a commercial semiconductor device modeling package. A number of LBIC maps are presented for different wafer processing conditions, with the results being explained using the simulation software. The experimental and calculated results bring to light a number of previously unreported characteristics associated with the LBIC phenomena, including the effect of junction depth, temperature, and grading of the junction region. In addition to the LBIC technique confirming the presence of an n⁺ region after RIE processing, it also provides information regarding the depth of the n⁺ region and lateral extent of the doping.     

Development of nuclear radiation detectors based on epitaxially grown thick CdTe layers on n<Superscript>+</Superscript>-GaAs substrates

A CdTe/n⁺-GaAs heterojunction diode for a room-temperature nuclear radiation detector has been developed and demonstrated. The heterojunction diode was fabricated by growing a 2–5-μm-thick iodine-doped n-CdTe buffer layer on the n⁺-GaAs substrates, followed by about 100-μm-thick undoped p-like single crystalline CdTe layer using metalorganic vapor-phase epitaxy. The n-type buffer layer was found to be essential to improve the junction property of the diode detector. The diode detectors exhibited good rectification property and had the reverse leakage currents typically from 1 μA/cm² to 5 μA/cm² at 40 V bias. The detector clearly demonstrated its energy resolution capability by resolving the 59.54-keV gamma peak from the ²⁴¹Am radioisotope during the radiation detection test.     

Planar p-on-n HgCdTe heterojunction mid-wavelength infrared photodiodes formed using plasma-induced junction isolation

Planar p-on-n HgCdTe heterojunction photodiodes have been fabricated using a plasma-induced type conversion process for device junction isolation. The technique is presented as a fully planar alternative technology to the commonly used mesa isolation structure. The starting material consisted of an indium-doped n-type mid-wavelength infrared (MWIR) HgCdTe absorbing layer that was capped by a 1-μm-thick wider bandgap arsenic-doped p-type layer. Junction-isolated p-on-n diodes were formed by selectively p-to-n type converting the p-type cap layer using a plasma process. Photodiode dark current-voltage measurements were performed as a function of temperature, along with noise and responsivity. The devices have cut-off wavelengths between 4.8 μm and 5.0 μm, exhibit diffusion-limited dark currents down to 145 K, give R₀A values greater than 1 × 10⁷Ω·cm² at 80 K and greater than 1 × 10⁵Ω·cm² at 120 K, and have negligible 1/f noise current at zero applied bias.     

Drift-diffusion theory of symmetrical double-junction diodes

Using numerical methods, we have calculated the current-voltage characteristics, energy contours and carrier distributions of a symmetrical double junction diode (n⁺nn⁺ and n⁺pn⁺). It is found that the I-V characteristics at low currents and voltages depend greatly on the doping concentration of the base region; at hihg currents, they do not. In that regime, the characteristics bunch together, and can be approximated with remarkable fidelity by the Mott-Gurney law for space-charge controlled conduction in solids. Characteristics are presented for different impurity densities and base widths.     

Electrical and luminescence properties of silicon-based tunnel transit-time light-emitting diodes p +/n +/n-Si:Er

The electrical and luminescence properties of silicon-based tunnel transit-time light-emitting diodes (LEDs) p ⁺/n ⁺/n-Si:Er, emitting under reverse bias on the p ⁺/n ⁺ junction in the breakdown regime, have been investigated. The room-temperature emission power at the wavelength λ ≈ 1.5 μm (∼5 μW), external quantum efficiency (∼10⁻⁵), and excitation efficiency of erbium ions (∼2 × 10⁻²⁰ cm² s) have been determined. At the same excitation efficiency, tunnel transit-time LEDs exhibit higher emission power in comparison with p ⁺/n-Si:Er diode structures. The experimental results are compared with the model predictions for these structures. The factors limiting the electroluminescence intensity and impact excitation efficiency for erbium ions in tunnel transit-time LEDs are discussed.     

Growth of very low arsenic-doped HgCdTe

Arsenic is known to be an amphoteric impurity that may occupy either sublattice in HgCdTe depending upon sample annealing. As an acceptor in low concentrations, it offers several features that are attractive for the fabrication of certain n + -on-p detector diode structures. The epitaxial growth of arsenic-doped HgCdTe from a Te-rich melt can fulfill the requirements for application in a variety of devices where low vacancy concentrations and low defect densities are critical requirements in minimizing dark currents. These devices may include the high operating temperature (HOT) detectors operated in a strong nonequilibrium and reverse bias mode to suppress the Auger-generated dark currents. For the materials’ growth process to be effective, the segregation coefficient determining the incorporation of arsenic from the Te-rich melt needs to be established. This coefficient was measured during these investigations and was observed to vary with arsenic concentration. Within the range of interest, this parameter varied between 8×10⁻⁶ and 1×10⁻⁴. These extremely small values limit the doping that can be achieved to <5×10¹⁶ cm⁻³ in the grown epifilm. Furthermore, the large addition of arsenic to the melt, necessitated by the extremely small segregation coefficients, leads to a condition where the concentration of arsenic in the liquid-phase epitaxy (LPE) nutrient melt exceeds that of cadmium. The melt chemistry, phase diagram, and epigrowth process fundamentally change as a result. This new epigrowth process was developed and tuned during these investigations. For acceptor levels at 1×10¹⁵ cm⁻³ and lower, the growth of arsenic-doped HgCdTe from a Te-rich LPE melt has been determined to be an extremely reproducible, powerful, and controllable technique.     

The p+n−n+ pulsed diode at extreme current densities—II: The forward pulsed case and its anomalous voltage response

The voltage transient response of the p⁺n^?n⁺ diode structure to a single intense current pulse in the forward direction is presented for current densities up to 10⁴ A/cm². The anomalous voltage response is studied by computer simulation of the device and compared with the experimental results. The response at these current densities becomes very dependent upon the carrier lifetimes and the recombination law chosen for the n⁺ region. At the larger current densities Avalanche generation and Auger recombination can exist simultaneously, yielding a larger than expected voltage across the device even as steady state is approached.     

Erbium ion electroluminescence in p ++/n +/n-Si:Er/n ++ silicon diode structures

Results of experimental studies of erbium ion electroluminescence in p ⁺⁺/n ⁺/n-Si:Er/n ⁺⁺ silicon diode structures grown by sublimation molecular-beam epitaxy are discussed. The distinctive feature of these structures is that the regions of electron flux formation of (n ⁺-Si) and impact excitation of erbium ions (n-Si:Er) are spaced. The influence of the n ⁺-Si layer thickness on electrical and electroluminescent properties of diodes was studied. It was shown that n ⁺-Si layer thinning causes the transformation of the structure breakdown mechanism from tunneling to avalanche. The dependence of the Er³⁺ ion electroluminescence on the thickness of the heavily doped n ⁺-Si region is bell-shaped. At the n ⁺-Si-layer doping level n ≈ 2 × 10¹⁸ cm^?3, the maximum electroluminescence intensity is attained at an n ⁺-Si layer thickness of ～23 nm.