Effective elastic constant theory of transverse wave interaction in a piezoelectric semiconductor

Small-signal low-frequency current gains of the npn and pnp transistor sections of high and low power thyristors were measured by a three-terminal technique. From their dependence upon current and temperature it was found that the saturation current dependence of the isolated centre junction primarily determines temperature stability. Current gain measured at a series of temperatures, and plotted para-metrically with anode current, qualitatively correctly predicts the temperature dependence of the two-terminal latching currents. Gold-doping predictably leads to a low current gain for the pnp section.     

A simple method for achieving immunity to internal noise signals in thyristors

The work presents an alternative solution—with respect to the conventional cathode shunts or MOS-controlled emitter shorts—for achieving virtual immunity to the parasitic action of displacement currents in power thyristors. The simple design/technological approach developed, based upon the novel double-interdigitated or two interdigitation levels (TIL) concept with a coarse geometry, offers a fair balance between technological simplicity/cost effectiveness and overall device performance.

Based upon the presented design guidelines, two sets of gold-doped thyristors with different geometrical configurations and current/voltage-handling capabilities were produced. The measurements performed on both sets of TIL-type thyristors have shown that the devices possess an extremely high value of the maximum permissible critical rate of rise of the forward anode voltage (static dV/dt capability) even under open-gate conditions. Unlike the thyristors using conventional emitter shorts, the TIL-type devices possess a good static and dynamic turn-on/latching sensitivity and have low on-state losses at high anode current densities. The main implications of developed concepts for power thyristors design/technology are also outlined in this work.     

Gate-assisted turn-off effect in TIL-type thyristors

The research reported in this work was focused on the turnoff performance of trial high-power gate-assisted turn-off thyristors (GATT's) based upon the novel double-interdigitated or two interdigitation levels (TIL) gate-cathode concept. The experiments were performed on high-voltage (2000 V) devices which were driven up to an anode current ofi_{T} = 500A. The test TIL GATT's were both gold-doped and normal (nongold,diffused). The investigations have shown that the application of a negative gate current of only 4 A leads to a reduction of the turn-off time iqby a factor of 3 and 4-4.5 in gold-doped and normal devices, respectively, at Tj= 100°C. At constant gate current, the dependence of tqon the anode current level tTwas found relatively weak. The additional experimental data provided in this work show clearly that sought-for benefits could be achieved by implementing the TIL pattern in power GATTs.     

Edge inversion channels and surface leakage currents in high-voltage semiconductor devices

It is shown that the electric field over the surface of semiconductor devices can be sufficient to induce edge inversion channels if the bias voltage is high and the surface charge density Q _s is low. In this case, the edge region of the devices containing the p-n-p structure (e.g., that of thyristors) functions as a planar p-channel MIS transistor with a combined gate and drain and the entire medium over the surface functions as the gate insulator. The current between the source and drain of this “edge MIS transistor” is the surface leakage current of the entire device. An analytical theory describing the current-voltage characteristic in the subthreshold mode is developed. It is shown that this new mechanism controls the total leakage current of high-voltage devices if |Q _s | and temperature T are small enough (|Q _s | < 4 nC/cm², T < 270 K and |Q _s | < 58 nC/cm², T < 600 K for silicon and silicon carbide devices, respectively).     

Characteristics of TIL GTO thyristors using no lifetime killers

The investigation reported in this work was focused on the main characteristics of the recently developed two interdigitation level (TIL) gate turn-off (GTO) thyristors, which use neither lifetime killers nor anode shorts. The advantages of these TIL GTO's with low on-state losses are outlined in comparison with their identical, yet gold-doped, counterparts. It is shown that, except for the turn-off time, the main electrical characteristics of TIL GTO's using no induced recombination centers are superior to those of similar gold-doped devices. The current-handling capability of the former under tough electrothermal ratings is also better than that of gold-doped devices up to a commutation frequency of 5 kHz. The results of this work demonstrated that sought-for benefits could be obtained in TIL GTO's which use neither induced recombination centers nor anode shorts.     

Fast soft recovery thyristors with axial lifetime profile fabricated using iridium diffusion

The paper presents experimental results on samples of fast soft reverse recovery thyristors with axial carrier lifetime gradient in the wide base, realised using combination of iridium diffusion with low dose of electron irradiation. Using this technique, fast thyristors of I_TAV=960 A, V_DRM=3 kV, turn-off time t_q≈110 μs and reverse recovery charge Q_rr≈700 μC, were fabricated. The softness factor t_f/t_s≈1 at −dI_T/dt=50 A/μs. Devices can be used in e.g. frequency converters based on the current source inverter.     

Pressure and composition dependence of high field instabilities in In As1−xPx alloys

Experimental and theoretical studies have been made of electron transport and hot electron effects in In As_1?xP_x as a function of alloy composition and hydrostatic pressure to 15 k-bar. Pulsed measurements of the current-voltage (I-V) characteristic up to the onset of current instabilities were made on H-shaped, epitaxial samples. To derive the velocity-field relationship, the electric field was related to V by making potential profile measurements and the electron velocity was determined from I by Hall mobility measurements at a magnetic field of 9 T. At atmospheric pressure and x < 0.3, the high-field instabilities were caused by avalanche multiplication and for x > 0.3 by the Gunn effect. The threshold field, F_T, was found to increase steadily with x from about 1 kV cm^?1 in In As to close to 9 kV cm^?1 in InP. In the avalanche region, (x < 0.3), increasing pressure and increasing x produced similar changes in both F_T and ν_T if 1 k-bar was set equivalent to 1% increase in phosphorus. In the Gunn region, despite the increasing threshold field, ν_T measured remained almost constant with composition. By contrast, with increasing pressure F_T remained almost constant and ν_T dropped about 16% in 15 k-bar. The results were simulated by Monte Carlo calculations of the velocity-field characteristics including an ionized impurity scattering corresponding to the low-field mobility of the samples used. Reasonable agreement was obtained for the magnitudes of F_T and ν_T and for their variations with pressure and composition. By reducing the impurity scattering to zero, estimates for the characteristics of the pure alloy were obtained. These indicated that ν_T increases from about 2.6 × 10⁷ cm s^?1 in InP to 3.05 × 10⁷ cm s^?1 in In As_0.7P_0.3, suggesting this may be a useful material for microwave devices. Analysis of the transition from avalanche break-down to Gunn effect gave values of the sub-band gap (ΔE_Γ?L) of 0.71 and 0.79 eV for In As_0.7P_0.3 and In As_0.79P_0.21 respectively.     

A measurement technique and algorithm for determining the n-p-n and p-n-p alphas of a thyristor

A new method has been developed for accurately measuring the forward-blocking characteristics of gate-turnoff (GTO) thyristors, and for converting these characteristics into plots of n-p-n and p-n-p gain as a function of anode current and anode voltage. Specifically, anode current and gate current are measured as functions of gate-to-cathode voltage at a fixed anode voltage over several orders of magni, tude of anode current. These data are used to determine the electron and hole components of anode current, which are, in turn, used to calculate αnpnand αpnpover the entire range of anode current of interest. Examples are given that show how junction shorts, low minority-carrier lifetime in the n-base, and anomalously low n-p-n gain are diagnosed in GTO thyristors. These new procedures have successfully diagnosed the causes of gate insensitivity in 95 percent of the devices to which they have been applied.     

Gate current flow in cylindrical thyristors with partially shorted cathodes—two and three terminal operation with inner and outer gate configuration—turn-on area

Following on the work of linear thyristors, the gate current flow in cylindrical thyristors is investigated with partially shorted cathodes. Once more the models employ single shorting “dots” (SD) for the two symmetrical configurations possible for the cylindrical geometry, inner gate—outer SD and inner SD—outer gate for a range of sheet resistance values (?/W) for the gate region.The non-linear differential equation governing gate current flow is given by y″+ξ^?1y′(y?1)?Cy = 0 (y = normalised gate current, ξ = normalised radial co-ordinate) with Non-Cauchy boundary conditions and the latter difficulty is overcome both for two and three terminal operation by similar methods previously employed, when solving for y(ξ) for a variety of device geometries and (?/W) values as well as bias conditions. The theory of turn-on area in terms of a critical cathode current density J_KB is also applied to this cylindrical model and expressions are obtained for the gate drive I_GD required to achieve a given turn-on area. Of particular interest are the plots of gate current flowing into the SD as a function of I_GD for a variety of (?/W) values as well as for the two possible gate/SD configurations.     

Increasing the current-handling capability of TIL GTO thyristors up to its limits—II. Experimental

The theoretical analysis and the developed design criteria for TIL GTO thyristors presented in the first part of this study (Paper I) are validated experimentally. The TO-220-packaged, high-voltage (V_DRM = V_RRM = 1000–1500 V) test TIL GTOs had a total cathode area of 8 mm², of which the area of deep-diffused cathode zones amounted to 3.5 mm². The implementation of optimized technological/geometrical ratios for TIL gate-cathode configuration yielded TIL GTO thyristors with a maximum controllable anode current of 55 A, which is the highest value of I_ATO reported thus far in the open literature for this class of GTOs (identical device area and case). All technological factors and physical effects underlying this achievement are analyzed in detail in this work. The current balancing between the two types of elementary p-n-p-n sections (standard and quasi-nonregenerative) constituting the vertical structure of the novel device is checked experimentally and the impact of this peculiar effect on current-handling capability of TIL GTOs is assessed both qualitatively and quantitatively. The boost of I_ATO up to its limits, ultimately dictated by the thermal impedance junction-to-case Z_thj?c TO-220-packages, was accompanied by a significant increase of the peak turn-off gain (10–20) of these devices at higher levels of anode current and by failure-safe operation of TIL GTOs at high commutation frequencies (up to hundreds of kHz) under heavy load conditions. The developed devices possess an excellent turn-on sensitivity and a high immunity to noise (high dV/dt capability). All the results of this work show clearly that sought-for benefits could be obtained by using the optimized double-interdigitated (TIL) gate-cathode pattern in GTO thyristors. The notation used is the same as in Paper I.     

Implementing the TIL Concept in high-power GTO's

This work reports the results obtained in the implementation of the novel two interdigitation level (TIL) gate-cathode configuration in high-voltage (2000 V), high-current (600 A), gate turn-off (GTO) thyristors. It is shown that the implementation of the TIL concept in high-power GTO's, while relaxing the trade-off between the doping/ width of the p base and the main electrical parameters, offers a fair balance between manufacturability ease/cost effectiveness and overall device performance. A distinct benefit obtained through the implementation of the TIL pattern in high-power GTO's is expressed by the ability of devices with an active area of only 1.7 cm²to safely switch off an anode current of 600 A with a practically usable operational turn-off gain Goffof 5-8. The low on-state voltage drop of gold-doped, high-power TIL GTO's is accompanied by a high nonrepetitive surge current capability. The trial devices possess a good latching/turn-on sensitivity accompanied by an immunity to noise (high dV/dt capability).     

The dV/dt capability of double-interdigitated (TIL) thyristors

This work presents an alternative solution, with respect to the conventional cathode-emitter shorts or MOS-controlled emitter shorts, for achieving virtual immunity to the parasitic action of displacement currents in power thyristors. The developed simple design/ technological procedure, based upon the novel double-interdigitated or two interdigitation level (TIL) gate-cathode configuration with a coarse geometry, offers a fair balance between technological simplicity/cost effectiveness and overall device performance. Based upon the developed design guidelines, two sets of gold-doped thyristors with different geometrical configurations and current-voltage handling capabilities were produced. The performed measurements have shown that both sets of TIL thyristors possess an extremely high value of the maximum permissible critical rate of rise of the off-state voltage (dV/ dt capability) even under open-gate conditions. When the gate is connected to the cathode, the TIL thyristors are practically immune to the action of displacement currents. Unlike thyristors using conventional emitter shorts, the TIL-type devices possess a good static and dynamic turn-on/latching sensitivity and have low on-state losses at high-current densities.     

Lateral current flow in thyristors with partially shorted cathodes—II: Three-terminal operation,theory of turn-on area,plasma spreading velocity and the effect of gold doping

The lateral current flow I_G(x) in the p-gate region of a thyristor under three-terminal operation in the high-impedance region is investigated, the cathode except where stated, being partially short-circuited. For the simple model employed it appears that a large fraction of the gate current drive flows out of the shorting dot (SD). In the region of high cathode bias, close to the gate contact, I_G(x) follows a very different—though admittedly estimated—course compared to the two-terminal case of paper (I). It falls in value with increasing distance from the gate contact until V_K the cathode junction voltage bias has fallen to such a low value that I_G(x) starts rising again similarly to the two-terminal case. Estimates are also made of V_K(x) and J_K(x) the cathode current density and a theory of the turn-on area is put forward based upon the assumptions of (a) a much faster n-p-n transistor response compared to the p-n-p section and (b) a critical cathode current density derived from the two-terminal (no SD) breakover condition. The influence of gold doping is surmised in keeping with the measured differences between gold-doped and nominally gold-free devices. Finally, as in paper (I) an expression for effective current gain is sought for three-terminal operation proving successful for an n-p-n transistor but more elusive for a thyristor structure. Nevertheless the equations graphically illustrate the influence of the SD in reducing the applied gate drive to an effective gate drive. Approximate analytical solutions are obtained for I_G(x), J_K(x) and turn-on area, the latter two also as a function of gate drive. This solution also yields important constants of the theory. Initial computer calculations confirm this.     

Temperature dependence of field-controlled thyristor characteristics

The dependence of the characteristics of field-controlled thyristors upon the ambient temperature has been examined in the range of -30 to 200°C. Unlike conventional thyristors, these devices have been found to continue to exhibit forward blocking capability up to the highest measurement temperature (200°C). In fact, it is shown here that the forward blocking capability as well as the blocking gain improve with increasing temperature with the usual scaling of the leakage current for power devices. The reverse blocking capability is also retained. The forward voltage drop of the device in the conducting state decreases with increasing temperature. This behavior is shown to be similar to that of conventional rectifiers and thyristors operated at high injection levels. Further, the force gate turn-off time of the devices has been found to increase with increasing temperature. This has been correlated with a measured increase in the minority-carrier lifetime. The results of this study demonstrate that field-controlled thyristors are capable of being operated at higher temperatures than conventional thyristors.     

Improved Schottky clamped (T/SUP 2/L) circuits

Al-Si Schottky clamped transistors used as fast switching signal devices or in integrated circuits are superior to gold-doped transistors for such parameters as low-level current gain, leakage current I/SUB CO/, and propagation delay t/SUB pd/. A digital application is used to show how some of these parameters can be optimized for a T/SUP 2/L circuit, providing high switching speed (t/SUB pd/ 4 to 5 ns) and a 40-percent better worst-case low-level noise margin than the usual gold-doped T/SUP 2/L circuit.     

Effect of transverse constant electric field on the electron interference effects related to the under-barrier penetration of quantum-mechanical current density in 2D semiconductor nanostructures

The effect of transverse constant electric field F on the under-barrier penetration of the local quantum-mechanical current density in a 2D semiconductor structure is theoretically studied. The structure represents two quantum wells with identical widths that are sequentially located along the propagation direction of electron wave: the first well has the rectangular cross section, and the second well exhibits a semi-infinite rectangular potential barrier with height V ₀ that is modified by the transverse electric field. When an electron wave whose energy is less than resulting height of the potential barrier V _eff is incident from the first well on the barrier under certain conditions, the coordinate-dependent exponentially decaying penetration of the local quantum-mechanical current density may take place under the barrier due to the interference of electron waves in the nanostructure. It is demonstrated that the penetration parameters depend on field strength F.     

基于再生长欧姆接触工艺的220 GHz InAlN/GaN 场效应晶体管

本文在蓝宝石衬底上研制了具有高电流增益截止频率(f_T)的InAlN/GaN异质结场效应晶体管 (HFETs)。基于MOCVD外延n -GaN欧姆接触工艺实现了器件尺寸的缩小,有效源漏间距(L_sd)缩小至600 nm。此外,采用自对准工艺制备了50 nm直栅。由于器件尺寸的缩小,V_gs= 1 V下器件最大饱和电流(I_ds)达到2.11 A/mm,峰值跨导达到609 mS/mm。小信号测试表明,器件f_T达到220 GHz、最大振荡频率(f_max)达到48 GHz。据我们所知,该f_T值是目前国内InAlN/GaN HFETs器件报道的最高结果。     

波导CO2激光器等离子体特性研究

本文首次报导了CO2波导激光器的等离子体特性。用双探针法测量了不同工作条件下的CO2波导激光器等离子体的电子温度,得到一系列确切的电子温度测量值。并且分析了电子温度与放电电流、工作气压和混合比之间的关系。     

A Far IR Study of NbN in the Normal and Superconductive State

A thin film of NbN (thickness t = 300 Å), has been deposited on an MgO and a Si wafer. Both samples have been studied by transmission from 10 or 20 to 120 cm^?1, and have exhibited one maximum of transmission at a given frequency like the classical superconductors as Pb, Sn or Hg in the superconductive state. From the Far IR experimental data, the characteristic temperature θ_c, and the gap frequency (ν_gap (θ) = 2 Δ (θ), Δ(θ) being the energy gap) are immediately obtained (for instance for the NbN / MgO sample, θ_c = 15.5 K; ν_g (5 K) = 39.7 cm^?1), and it is seen that $\frac{{{\text{2}}\vartriangle (4{\text{K)}}}}{{{\text{k}}_{\text{B}} \theta _c }} \approx 3.5$ as expected from the BCS theory for a weak coupling. To fit the data we had to adjust only two additionnal parameters: collision and plasma frequency, ν_c (θ) and ν_p (including all carriers). At θ = 5 K, thebest fit for the NbN / MgO sample is obtained with ν_c = 371 cm^?1 and ν_p = 12,600cm^?1.     

Spectroscopy in propyne and ethyl-Chloride by means a tunable CO2 RF laser

Some lines in ν5 band of propyne (CH₃CCH) and many strongest lines in the ν9 band of ethyl- Chloride (C₂H₅Cl³⁵ A-type) are measured and identified, giving a new set of spectroscopic constants. In particular the ethyl-Chloride set allows to assign all the FIR transitions reported in literature.