Current-induced Degradation Research Articles

Stress Effect on Current-Induced Degradation of Be-Doped AlGaAs/GaAs Heterojunction Bipolar Transistors

The effect of stress on the current-induced degradation of current-voltage characteristics in AlGaAs/GaAs heterojunction bipolar transistors with Be-doped base layers is investigated. Transistors with different orientations of the emitter mesa and different thicknesses of the passivation film are bias tested at room temperature. The results are compared with the stress distributions along the emitter-base junction obtained from a two-dimensional calculation using the boundary element method. It is found that the degradation is caused by the diffusion of Be under high-current density operations and that the flux of Be diffusing from the base layer to the emitter layer is strongly related to the stress distributions around the periphery of the emitter-base junction.

Stability of carbon and beryllium-doped base GaAs/AlGaAs heterojunction bipolar transistors

GaAs/AlGaAs heterojunction bipolar transitors (HBTs) utilizing highly Be-doped base layers display a rapid degradation of dc current gain and junction ideality factors during bias application at elevated temperature. For example, the gain of a 2×10 μm2 device with a 4×1019 cm−3 Be-doped base layer operated at 200 °C with a collector current of 2.5×104 A cm−2 falls from 16 to 1.5 within 2 h. Both the base emitter and base collector junction ideality factors also rise rapidly during device operation, and this current-induced degradation is consistent with recombination-enhanced diffusion of Be interstitials producing graded junctions. By sharp contrast, devices with highly C-doped (p=7×1019 cm−3) base layers operated under the same conditions show no measurable degradation over much longer periods (12 h). This high degree of stability is most likely a result of the fact that C occupies the As sublattice, rather than the Ga sublattice as in the case of Be, and also has a higher solubility than Be. The effect of nearby implant isolated regions in promoting Be diffusion is also reported.

Recombination-enhanced impurity diffusion in Be-doped GaAs

Recombination-enhanced impurity diffusion (REID) in Be-doped GaAs has been observed for the first time. Current-induced degradation of tunnel diodes has been investigated. The Be diffusion under forward bias is enhanced by a factor of about 1015 at room temperature, and the activation energy for the diffusion is reduced from 1.8 eV for thermal diffusion to 0.6 eV for REID. The RElD of Be, in which the energy released on minority-carrier injection at the recombination center could enhance the diffusion, is thought to be the origin of the degradation.

On the investigation of degradation mechanisms in ultrahigh performance GaAs heterojunction bipolar transistors

Recently, current-induced degradation in the form of V/sub BE/ shifts has been reported when the heterojunction is stressed under high-level forward current injection. Although the V/sub BE/ shift is an indication of device parameter change, the degradation mechanisms cannot be readily identified. An approach is presented that uncovers the device degradation mechanisms by measuring the inverted mode I/sub C/ at room temperature and the forward mode I/sub B/ at low temperature. The correlation between the change in the inverted I/sub C/ and an anomalous component (tunneling current) of I/sub B/ is observed and attributed to beryllium interstitial diffusion into substitutional sites.

Measurement and characterization of voltage- and current-induced degradation of thin-film photovoltaic modules

Abstract A number of important degradation mechanisms that determine the life of thin-film photovoltaic (PV) modules are driven by voltages and currents, either internal to the module, or between the module and its external mounting environment. Two important mechanisms are electromigration and electrochemical corrosion. Electromigration is current-induced diffusion of electrical conductors, such as the cell back metallization, at high current densities approaching 10 6 A cm −2 of conductor cross-section. Electrochemical corrosion is the transport of ionic elements in the presence of applied electric field, and in the case of PV modules is generally associated with corrosion of internal cell materials as a result of leakage currents from the cell string to the module exterior. This paper reviews the status of JPL's research into these mechanisms as they affect thin-film modules of amorphous silicon (a-Si) and CdTe.

The mechanisms of current-induced degradation in a GaAs light-emitting diode : Edward F. Thomas Jr.13th Annual Proc. Reliability Physics Symposium, Nevada. 1975 p. 215

The mechanisms of current-induced degradation in a GaAs light-emitting diode : Edward F. Thomas Jr.13th Annual Proc. Reliability Physics Symposium, Nevada. 1975 p. 215