Effect Of Junction Capacitance Research Articles

Junction Diameter Dependence of Oscillation Frequency of GaN IMPATT Diode Up to 21 GHz

An experimental study on the effects of junction capacitance and current density on the oscillation characteristics of GaN single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes were carried out using GaN p+-n abrupt junction diodes of various diameters, 200, 150, and 100 μm, with a depletion layer width of 2 μm. The fabricated diodes showed a clear avalanche breakdown at 315 V and a pulsed microwave oscillation with a peak output power exceeding 30 dBm. The oscillation frequency depended on junction diameter and current density. It was widely modulated from 8.56 to 21.1 GHz with decreasing junction diameter and increasing current density. The highest oscillation frequency was obtained with a current density of 13.8 kA/cm2 and a junction diameter of 100 μm. A numerical calculation based on Read-type small-signal theory was carried out and found to well explain the experimental results.

High-frequency characteristics of GaAlAs injection lasers

This paper discusses the results of an extensive experimental study of the high-frequency characteristics of several commercial (GaAl)As injection lasers. The lasers tested included the Hitachi buried heterostructure (BH), the Hitachi channel substrate planar (CSP), the Mitsubishi transverse junction stripe (TJS), the General Optronics stripe (GO), and the RCA constricted double heterostructure (CDH). We find that the maximum practical analog modulation frequency f o is in the range of 5 GHz. This practical modulation frequency is limited by a combination of laser-relaxation resonance, laser parasitics, and drive current necessary for long-life operation. The relationship between laser-relaxation oscillation resonance frequency f o and drive current can be expressed as f_{o} = K(I/Ith - 1)^{1/2} GHz where I and Ith are the laser drive and threshold currents, respectively. The value of K is experimentally determined to lie in the range 3.0 K j and a capacitance C j . The product of R_{j}C_{j} has been experimentally determined for both the Hitachi CSP and BH laser and lies in the range of 1-1.1 \times 10^{-10} s. The effect of laser mount and packaging can also be included in the equivalent circuit by the addition of series inductors and shunt capacitors. Lastly, all injection lasers studied displayed a dip in the small signal modulation response prior to the onset of the relaxation oscillation resonance. In particular, there is a pronounced dip even for lasers with good lateral carrier confinement at dc, such as the buried heretostructure (BH). Previous workers have attributed the dip in the modulation response as resulting from either lateral diffusion of injected carriers, or the effect of junction capacitance. Our experimental results indicate that while the effect of the junction capacitance may play some role in explaining the dip for the BH laser, it is not the dominant mechanism. We speculate that lasers with good lateral carrier confinement at dc (BH) may suffer a significant degradation of carrier confinement at gigahertz rates. A simple qualitative model is proposed to explain this mechanism and methods for reducing the effect are discussed.

High-Frequency Characteristics of GaAlAs Injection Lasers

This paper discusses the results of an extensive experimental study of the high-frequency characteristics of several commercial (GaAl)As injection lasers. The lasers tested included the Hitachi buried heterostructure (BH), the Hitachi channel substrate planar (CSP), the Mitsubishi transverse junction stripe (TJS), the General Optronics stripe (GO), and the RCA constricted double heterostructure (CDH). We find that the maximum practical analog modulation frequency f/sub o/ is in the range of 5 GHz. This practical modulation frequency is limited by a combination of laser-relaxation resonance, laser parasitic, and drive current necessary for long-life operation. The relationship between laser-relaxation oscillation resonance frequency f/sub o/ and drive current can be expressed as f/sub o/ = K(I/I/sub th/ - 1)/sup 1/ 2/ GHz where I and I/sub th/ are the laser drive and threshold currents, respectively. The value of K is experimentally determined to lie in the range 3.0< K < 5.3 GHz for all the lasers studied. An equivalent circuit for the injection laser for frequencies in the range of 100 MHz-6 GHz has been experimentally determined. We find that the isolated injection laser can be modeled by the parallel combination of a resistance R/sub j/ and a capacitance C/sub j/. The product of R/sub j/C/sub j/ has been experimentally determined for both the Hitachi CSP and BH laser and lies in the range of 1-1.1 X 10/sup -10/s. The effect of laser mount and packaging can also be included in the equivalent circuit by the addition of series inductors and shunt capacitors. Lastly, all injection lasers studied displayed a dip in the small signal modulation response prior to the onset of the relaxation oscillation resonance. In particular, there is a pronounced dip even for lasers with good lateral carrier confinement at dc, such as the buried heterostructure (BH). Previous workers have attributed the dip in the modulation response as resulting from either lateral diffusion of injected carriers, or the effect of junction capacitance. Our experimental results indicate that while the effect of the junction capacitance may play some role in explaining the dip for the BH laser, it is not the dominant mechanism. We speculate that lasers with good lateral carrier confinement at dc (BH) may suffer a significant degradation of carrier confinement at gigahertz rates. A simple qualitative model is proposed to explain this mechanism and methods for reducing the effect are discussed.

Effect of Junction Capacitance on the Rise Time of LED's and on the Turn-on Delay of Injection Lasers

The space-charge capacitance of the forward-biased junction has been found to play a major role in (i) the apparent rise time of the emission from small-area, high-radiance led's and (ii) the apparent turn-on delay of stripe-geometry dh-structure laser diodes. For a zero-bias capacitance of 200 pF, a typical value for such devices made by oxide-masking techniques, the measured rise time of an led that is fully turned on and the turn-on delay time of injection lasers may be as much as twice the limitation imposed by the spontaneous carrier recombination time. A proposed method to reduce these delays by preshaping the driving pulse is analyzed, and a reduction of the delay by a factor of 2 or better is predicted. These results are in agreement with experiments.

Punchthrough and the Tunneling Cryotron

The effect of junction capacitance on the behavior of the Josephson tunneling cryotron is considered and certain problems which may arise in high-speed applications are described.