30-nm two-step recess gate InP-Based InAlAs/InGaAs HEMTs

Two-step recess gate technology has been developed for sub-100-nm gate InP-based InAlAs/InGaAs high-electron mobility transistors (HEMTs). This gate structure is found to be advantageous for the preciseness of the metallurgical gate length as well as a comparable stability to the conventional gate structure with an InP etch stop layer. The two-step recess gate is optimized focusing on the lateral width of the gate recess. Due to the stability of the gate recess with an InP surface, a laterally wide gate recess gives the maximum cutoff frequency, lower gate leakage current, smaller output conductance and higher maximum frequency of oscillation. Finally, the uniformity of the device characteristics evaluated for sub-100-nm HEMTs with the optimized recess width. The result reveals the significant role of the short channel effects on the device uniformity.     

Analysis of hot carrier transport in AlGaAs/InGaAs pseudomorphicHEMTs by means of electroluminescence

The carrier transport phenomena occurring in pseudomorphic AlGaAs/InGaAs HEMTs biased in the on-state impact-ionization regime is analyzed in this paper. We confirm the presence, in the electroluminescence spectra of pseudomorphic HEMTs, of a dominant contribution due to electron-hole recombination and we identify a composite peak due to recombination of cold carriers. We analyze the recombination peak using a high-resolution monochromator, which reveals the fine structure due to transitions between electron and hole subbands in the channel quantum well, thus providing useful data concerning the properties of the InGaAs HEMT channel. We also demonstrate that recombination between nonenergetic electrons and holes occurs in the gate-source region, as already observed in InAlAs/InGaAs HEMT's on InP. This recombination emission is superimposed to a less intense contribution mostly coming from the gate drain region. This contribution has a nearly Maxwellian distribution which extends to fairly high energies (>3 eV) and has equivalent temperatures in the 1000-3000 K range. Finally we show evidence of recombination in the AlGaAs layers (observed at high electric field), which demonstrates, in these devices, real space transfer of both electrons and holes     

Degradation mechanisms in 2 W MESFETs

Biased life tests and thermal storage at different temperatures have been performed on 2 W GaAs MESFETs from two different suppliers. Failure modes and mechanisms are correlated to device technology and are thermally activated. In samples with Au/Pd/Ti gate metallization we observed a decrease of I_dss current and an increase of the gate diode reverse current. The former is related to the gate-semiconductor interaction, whereas annealing of GaAs surface states is responsible for the latter, which can cause the device burn-out. These degradations exhibit activation energies of 1 eV and 1.5 eV, respectively. In samples with Al gate metallization, we measured an increase of parasitic resistances possibly deriving from a degradation of the ohmic contacts.     

Transiently triggered latch-up in cmos twin-tub and epitaxial technologies

We present in this work an analysis of transiently triggered latch-up in test-structures fabricated using a twin-tub process implemented on two different substrates: a p-type and a p p⁺ epitaxial one. Steady-state electrical characterization confirmed the well-known increased latch-up resistance of epitaxial structures with respect to standard ones. In this paper it is shown that, depending on the chosen electrical configuration, when latch-up is transiently triggered, epitaxial structures may have dynamic triggering currents lower than twin-tub ones. The influence of some layout variables on turn-on threshold voltage has been investigated for all samples.     

A short-term high-current-density reliability investigation ofAlGaAs/GaAs heterojunction bipolar transistors

In high current and power density applications of AlGaAs/GaAs heterojunction bipolar transistors (HBT's), reliability is a critical issue. Therefore, in this letter we show results of a fundamental investigation on the temperature and current dependence of the fast initial rise of the dc-current gain (burn-in), which takes place during stress at current densities beyond those of today's applications. We find that the burn-in occurs at lower device junction temperatures (135°C) than previously reported in literature, and that it depends linearly on the current density. An activation energy of 0.4 eV is extracted for the burn-in effect     

Recovery of low temperature electron trapping in AlGaAs/InGaAsPM-HEMTs due to impact-ionization

The dc behavior of AlGaAs/InGaAs PM-HEMTs has been Investigated at a low temperature. Two different failure modes have been identified according to bias conditions, consisting of: (a) a dramatic collapse in the drain current I_D, and (b) a considerable shift in the threshold voltage V_T. I_D decrease is due to trapping of electrons in deep levels in the gate-drain region, while trapping under the gate is responsible for V_T shift. At high V_DS a recovery of the dc device characteristics is observed, due to impact-ionization phenomena     

Trapped charge modulation: a new cause of instability inAlGaAs/InGaAs pseudomorphic HEMT's

A new degradation mechanism of PM-HEMT's subsequent to hot electron stress tests or high temperature storage tests is presented. A noticeable increase in drain-to-source current, I_DS, is observed after the tests. We show that this I_DS variation is slowly recoverable and is correlated with the presence of deep levels in the device. Stress tests cause a variation of trapped charge. Trapping of holes created by impact-ionization and/or thermally stimulated electron detrapping induce a variation of the net negative trapped charge, leading to a decrease in the threshold voltage, V_T and a consequent increase in I_DS. The correlation between g _mΔV_T and ΔI_DS clearly demonstrates that the variation of trapped charge induced by hot electron tests is localized under the gate     

High temperature electro-optical degradation of InGaN/GaN HBLEDs

This paper presents a study of the high temperature degradation of high brightness light emitting diodes (HBLEDs) on gallium nitride. Two different families of devices, from two leading manufacturers, have been submitted to thermal stress: during treatment, the optical and electrical characteristics of the devices have been analyzed. Degradation modes detected after stress have been (i) operating voltage increase, (ii) output power decrease, (iii) modifications of the spectral properties. The degradation of the electrical and optical characteristics of the devices were found to have different kinetics: this fact indicates that optical power (OP) loss is not strongly related to the degradation of the electrical parameters of the LEDs. On the other hand, spectral analysis indicated that OP loss is strongly related to the decrease of the phosphors-related yellow emission band. Microscopic analysis showed that this effect can be ascribed to the carbonization of the package and phosphorous material. A degradation of the transparency of the top-side ohmic contact has been also detected after stress: these mechanisms are thought to be responsible for the detected OP decrease. OP decay process has been found to be thermally activated, with activation energy equal to 1.5 eV.     

Extensive Analysis of the Degradation of Blu-Ray Laser Diodes

This letter describes an analysis of the degradation of InGaN-based laser diodes. The influence of current, temperature, and optical power level on the degradation kinetics has been analyzed by means of a wide set of stress tests carried out under different operating conditions. We demonstrate the following: 1.) the degradation rate is strongly related to the operating current level; 2.) high-temperature stress does not determine significant degradation of lasers characteristics; and 3.) the intensity of the optical field does not significantly influence the degradation rate. Degradation process is found to be electrothermally activated and is ascribed to the increase of the nonradiative recombination rate in the active layer, with subsequent decrease of the efficiency of the devices.     

Quality of minimally processed red chicory (Cichorium intybus L.) evaluated by anthocyanin content,radical scavenging activity,sensory descriptors and microbial indices

Changes in the quality of minimally processed red chicory (Cichorium intybus L.) were studied during storage in a polyvinyl chloride (PVC) film and in a mono‐oriented polypropylene (OPP) film at 4 °C. The maximum limit of 5 × 10⁷ CFU g^?1 for mesophilic aerobic bacterial count was attained after 4 days using the PVC film and after 4.5 days using the OPP film. The loss of fruity aroma occurred after 3 days in the products stored in PVC but not in those stored in OPP. In spite of microbial growth, no off‐odour was perceived by trained panellists. Storage in PVC slightly decreased the contents of cyanidin 3‐O‐malonyl glucoside, total phenolics and antioxidant activity, whereas these parameters increased upon storage in OPP. When red chicory heads subjected to mild stress in the field were minimally processed, OPP packaging decreased the microbial growth with respect to PVC, but antioxidants were degraded in both conditions.