InP-based Heterostructure Bipolar Transistors Research Articles

Passivation of InP-based HBTs

The surface effects, the (NH 4) 2S and low-temperature-deposited SiN x passivations of InP-based heterostructure bipolar transistors (HBTs) have been investigated. The surface recombination current of InP-based HBTs is related to the base structures. The (NH 4) 2S treatment for InGaAs and InP removes the natural oxide layer and results in sulfur-bonded surfaces. This can create surface-recombination-free InP-based HBTs. Degradation is found when the HBTs were exposed to air for 10 days. The low-temperature-deposited SiN x passivation of InGaAs/InP HBTs causes a drastic decrease in the base current and a significant increase in the current gain. The improvement in the HBT performance is attributed to the low deposition temperature and the effect of N 2 plasma treatment in the initial deposition process. The SiN x passivation is found to be stable. S/SiN x passivation of InGaAs/InP HBTs results in a decrease in the base current and an increase in the current gain. The annealing process can cause the base current to decrease further and the current gain increase.

Effect of UV-ozone oxidation on the device characteristics of InP-based heterostructure bipolar transistors

In this letter, we report the effect of UV-ozone treatments on the electrical characteristics of InGaAs/InP heterostructure bipolar transistors (HBTs). For treatments of less than 10 min, the HBT’s current gain increased with the UV-ozone exposure. This improvement is attributed to a passivation of the extrinsic base. For exposures longer than 10 min, the current gain is reduced. An increase of the base collector leakage current, leading to a degradation of the HBT’s breakdown voltage, was observed after only about 2 min of UV-ozone treatment.

Passivation of InP-based HBTs

The passivation of the exposed semiconductor surfaces in a device is necessary to ensure good device performance. In this study we examine how different surface treatments and geometric device designs can be used to improve the dc performance of InP-based heterostructure bipolar transistors. We show how sulphur and UV-ozone treatment improves the performance of large-area devices and illustrate the effects of the treatment through XPS measurements on the semiconductor surfaces. We also demonstrate that a combination of UV-ozone+HF can lead to improved performance of small, high-frequency devices. This approach is contrasted with results using a layer structure with a thin emitter, where the emitter is left on the device to self-passivate the base surface. In this case the thin emitter layer on the base is depleted and no passivation treatment is needed.

Passivation of InP-Based Heterostructure Bipolar Transistors in Relation to Surface Fermi Level

The effect of surface Fermi level position on dc-characteristics of InP-based heterostructure bipolar transistors (HBT) is reported. The Fermi level of an InP surface covered with silicon oxide was located at an energy position close to the conduction band minimum of InP. This implies that an electron accumulation layer forms at the interface, which acts as a surface leakage path. The HBT passivated with silicon oxide films showed large excess base current and poor current gain. In contrast, the Fermi level position at the silicon nitride/InP interface was found to be near the midgap, and no electron accumulation layer was formed at the interface. The HBT passivated with silicon nitride film showed excellent dc characteristics with very small, excess base current.

Electrical stress damage reversal in non-passivated fully self-aligned InP HBTs by ozone surface treatment

The authors report that the degradation of device characteristics due to electrical stressing in non-passivated fully self-aligned InP-based heterostructure bipolar transistors (HBTs) can be reversed by a simple surface treatment in ozone. The technique is demonstrated on MOCVD-grown InP/GaAs0.51Sb0.49/InP double heterostructure bipolar transistors (DHBTs) with a C-doped base, and on conventional MBE-grown InP/Ga0.47In0.53As single heterostructure bipolar transistors (SHBTs) with a Be-doped base. This is the first report of the reversibility of bias stress damage in the extrinsic region of III-V HBTs: the experiments presented confirm that stress damage occurs at the exposed emitter periphery, thus explaining the success of emitter ledge passivation techniques.

Ultrahigh-Speed InP/InGaAs Double-Heterostructure Bipolar Transistors and Analyses of Their Operation

Novel hexagonal emitters are proposed for heterostructure bipolar transistors (HBTs) with a base-metal-overlaid emitter-base self-alignment structure to reduce parasitic effects. Two different layer structures for InP/InGaAs double-heterostructure bipolar transistors (DHBTs) that can more fully utilize the inherent potential of the materials are used to enhance unity current gain cutoff frequency, f T, and maximum oscillation frequency, fmax . On a wafer with a 180-nm-thick collector, a transistor with a 20-µ m2 hexagonal emitter electrode shows an f T of 230 GHz and an fmax of 147 GHz, while with a 4-µ m2 hexagonal emitter electrode the corresponding values are 225 GHz and 241 GHz. fmax of 300 GHz is achieved for a transistor with a 4-µ m2 emitter electrode and a 330-nm-thick collector. Transistor operation is analyzed using a simple but appropriate small-signal equivalent circuit model of a transistor that includes internal and external base/collector capacitances and yields good estimates of the measured scattering (s-) parameters. Even in these InP-based (D)HBTs, the internal collector capacitance increases with collector current density due to the Kirk effect which degrades performance. In thin-collector (D)HBTs, the increase in the internal collector capacitance is suppressed, which increases the collector current density at which the transistor can operate normally, and f T is increased by both transit time reduction and high-collector-current operation.

Highly doped galnAs using diethylberyllium by MOCVD for InP-based heterostructure bipolar transistor applications

Diethylberyllium has been used to produce high hole concentrations in latticematched Galnas grown by metalorganic chemical vapor deposition (MOCVD). Doping concentrations from p = 1 × 1019 up to 7.7 × 1019 cm−3 have been achieved at 500°C. To our knowledge, this is the highest doping level achieved by MOCVD in this material system. Secondary ion mass spectroscopy analysis showed a significant inclusion of oxygen in the as-grown material. Using beryllium-doped Galnas as the base layer, we have demonstrated InP-based heterostructure bipolar transistors. This shows diethylberyllium to be a promising p-type dopant for MOCVD applications.