The reliability of InGaP/GaAs N-p-n HBTs with different base metal contact systems (Au/Zn/Au, Ti/Au, Ti/Pt/Au and the novel Ti/ZrB2 /Au) under current and temperature stress is studied in this paper. We further report results of current stress on three p-GaAs doping impurities namely Zn, Be- and C. The effect of O+/H + and O+/He+ ions, used in the fabrication of planar self-aligned HBTs, is also investigated in the stability of device dc current gain. The instability phenomena typical of each factor and their effects on the HBT characteristics are reported

The reliability of InGaP/GaAs N–p–n heterojunction bipolar transistors (HBTs) with different base metal contact systems (Au/Zn/Au, Ti/Au, Ti/Pt/Au and the novel Ti/ZrB2/Au) under current and temperature stress is studied in this paper. We further report results of current stress on three p-GaAs doping impurities namely Zn, Be and C. The effect of O+/H+ and O+/He+ ions, used in the fabrication of planar self-aligned HBTs, is also investigated in the stability of device dc current gain. The instability phenomena typical of each factors and their effects on the HBT characteristics are reported.

The results of comparative investigations of the noise spectra of AlGaAs/GaAs HBTs with the optically transparent indium tin oxide (ITO) emitter contact and with the ordinary (opaque) emitter contact are presented. The measurements were carried out in the dark and under illumination in different transistor configurations and at different currents. This made it possible to detect the 1/f noise that is generated at the ITO contact and that is absent at the ordinary contact. It has been revealed that not only the emitter contact noise but also the noise generated in the emitter and even in the collector junctions of the HBTs with ITO contacts are much higher than in the devices with the ordinary contacts. It is also found that the excess noise of the base current in the devices of both types is much lower than in the AlGaAs/GaAs HBTs described in the literature and, hence, the HBTs investigated have improved noise performance for broad band circuit application.

A wide range of base ohmic contacts have been studied to determine each of their suitability for usage in InGaP/GaAs HBTs for operation at high temperature. A novel base ohmic contact using Ti/ZrB/sub 2//Au has been developed with ZrB/sub 2/ as a barrier layer to prevent Au indiffusion from the contact layer to the base region. Current stress at high temperature on these HBTs show that the devices with this novel contact remain unchanged beyond 20 hours whereas devices with conventional contacts show clear signs of degradation after only a few hours of stress.

The spectra of different excess noise sources are measured and analysed in AlGaAs/GaAs heterophototransistors with the transparent ITO emitter contact in the dark and under illumination. The 1/f (or burst) fluctuations of the tunnel-recombination component of the base current are shown to be the main source of the excess noise observed. The wide scatter of the noise data for different devices as well as the saturation of the noise level in a given device at the high current region appear to be typical for this noise. Its cut-off frequency determined for the floating base mode of operation is found to vary from 250 kHz to 30 MHz for different samples and at different collector currents. High doping levels of the emitter and base regions are considered as the main reason for the noise observed.

The electrical, optical and spectral responses of optically transparent emitter AlGaAs/GaAs and InP/InGaAs heterojunction phototransistors (HPTs) fabricated using indium tin oxide (ITO) are compared. Both these HPTs showed significantly increased optical responsivities while the electrical characteristics were similar to their respective opaque counterparts. Responsivities of 2.5A/W at 630nm for the AlGaAs/GaAs and 5.4A/W at 780nm and 30A/W at 1310nm for the InP/InGaAs HPTs were obtained. The spectral responses of these phototransistors were simulated and compared with the measured results for the first time. Good correlation between the experiments and the theoretical models were obtained in both cases. Moreover, the use of a thin film of indium between the ITO and n(+)-GaAs contact layers for the AlGaAs/GaAs HPTs was studied and the specific contact resistance was found to be an order of magnitude superior to the ITO/n(+)-GaAs contacts without degrading its excellent optical transmittance properties.

A comparison between MOCVD grown AlGaAs/GaAs and InGaP/GaAs HBTs showed a relatively constant DC current gain as a function of temperature upto 300/spl deg/C for the latter devices. A novel high temperature ohmic contact using ZrB/sub 2/ diffusion barrier has been developed and found to be suitable for HBTs operating at elevated temperatures. This barrier has been successfully employed in the fabrication of InGaP/GaAs HBTs which operated at 200/spl deg/C for 18 hours without any significant change to device performance.

The electrical, optical and spectral responses of optically transparent emitter InP/InGaAs heterojunction phototransistors (HPTs) fabricated using Indium Tin Oxide (ITO) are presented. These HPTs showed significantly increased optical responsivities while the electrical characteristics were similar to their respective opaque counterparts. Responsivities of 28A/W at 1310nm for the InPhGaAs HPTs were obtained. The spectral responses of these phototransistors were simulated and compared with the measured results and good correlation between the experiments and the theoretical models were obtained. Introduction : There has been renewed interest in the usage of phototransistors as detectors in OEICa, particularly in heterojunction phototransistors ( 1,2). HBTs fabricated using the InPhnGaAs material system has numerous advantages over its AlGaAdGaAs counterpart; as well as their -suitability for usage with long haul optical fiber telecommunications systems as near infra red detectors, we have shown that the InPhGaAs HBTs exhibit a lower turn on voltage (0.1 - 0.2V) than the GaAs-based HBTs (= 0.7V) (3) making them an ideal candidate for low power circuit applications such as mobile telecommunications. The coupling efficiency of a heterojunction phototransistor, HPT, can be significantly improved by using a transparent emitter contact thereby raising the -overall gain-bandwidth of the device correspondingly. We have successfully fabricated InPhGaAs HPTs using transparent Indium Tin Oxide (EO). The electrical, optical and spectral responses of these devices were measured and compared to their opaque counterparts. The transparent devices showed significantly increased optical responsivities while their electrical characteristics were 3imilar to the opaque devices. The spectral responses of these phototransistors were simulated and compared with the measured results. Good correlation between the experiments and the theoretical models were obtained.

A comparison of the electrical performance of InP/InGaAs HBTs is made with the much studied AlGaAs/GaAs and InGaP/GaAs material systems. This is followed by the presentation of a transparent emitter HBT fabricated using indium tin oxide (ITO) as the ohmic contact; this shows similar electrical characteristics to the opaque counterparts and enhanced optical responsivities.

An optically transparent emitter InP/InGaAs heterojunction phototransistor (HPT) fabricated using Indium Tin Oxide (ITO) as the ohmic contact is presented for the first time; these devices show similar electrical characteristics to their opaque emitter counterparts and enhanced optical responsivities (5.4 A/W at 780 nm wavelength). Measured spectral response suggests responsivities of up to 30 A/W and 22 A/W at /spl lambda/=1310 nm and 1550 nm respectively.< >

The electrical, optical and spectral responses of optically transparent emitter InP/InGaAs heterojunction phototransistors (HPTs) fabricated using Indium Tin Oxide (ITO) are presented. These HPTs showed significantly increased optical responsivities while: the electrical characteristics were similar to their respective opaque counterparts. Responsivities of 28 A/W at 1310 nm for the InP/InGaAs HPTs were obtained. The spectral responses of these phototransistors were simulated and compared with the measured results and good correlation between the experiments and the theoretical models were obtained

The authors report what they believe to be the first successful fabrication of an InGaAs/GaAs vertical-cavity surface emitting laser (VCSEL) using optically transparent indium-tin-oxide (ITO) ohmic contacts to p- and n-type regions of the laser. Threshold current densities J(th) are similar to those lasers fabricated from the same wafer using conventional ohmic contacts.

Excellent test ITO/n-GaAs Schottky diodes (ideality factor=1.07) have been fabricated by RF sputtering and this process has been optimised to produce high transmission (>90%), low resistivity (<2×10-5 Ωcm) and low leakage (<3 nA), responsivity=0.4A/W. These devices are designed to be monolithically integrated with HBTs to form fast photoreceivers for operation in the 800 nm wavelength for local communication networks

Optically transparent low resistivity Indium Tin Oxide (ITO) ohmic contacts to both n- and p-type GaAs have been successfully investigated. Contacts are featureless and may be used in surface emitting lasers and other optoelectronic devices