Low-Frequency Noise Measurements of Alxga1-Xas/Inyga1-Y as/Gaas High-Electron-Mobility Transistors

Low-frequency noise measurements have been performed in the linear range of the I-V characteristics of pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As/GaAs high electron mobility transistors (HEMTs) grown by molecular beam epitaxy with different channel thicknesses. The results obtained show that the 1/f noise in such devices depends greatly on channel thickness. It is controlled by the penetration of the electron wavefunction into the barrier as well as by Coulombic effects for thin channels and by the increase in dislocation concentration for thick ones. Generation-recombination (G-R) noise is also present. It is mainly due to real-space transfer of electrons between the two-dimensional electron gas in the channel and the conduction band minimum in the AlxGa1-xAs barrier. Similar results were obtained for the G-R noise of Al0.22Ga0.78As/In0.20Ga0.8As/GaAs, Al0.3Ga0.7As/GaAs, and Al0.48In0.52As/In0.47Ga0.53As/lnP HEMTs. (C) 1995 American Institute of Physics

Investigation of DX centers in modulation-doped field-effect transistor-type Al0.3Ga0.7As/GaAs heterostructures using a fourier-transform deep level transient spectroscopy system

Al0.3Ga0.7As:Si/GaAs modulation-doped field-effect transistor-type heterostructures were grown using two different growth temperatures (500 and 620 degrees C) and three doping modes (delta-doping, pulse-doping, and uniform-doping). Deep level transient spectroscopy (DLTS) measurements were performed on these structures using a new Fourier-analysis method. Up to four DLTS peaks, related to the different possible configurations of the nearest Al and Ga neighbors around each DX site, were observed. Both the growth temperature and the doping-mode are found to affect the DLTS spectra, in particular the number of observed peaks and their width. These results are interpreted in terms of the different mobilities of the Si doping atoms on the surface during growth

Optimum channel thickness of Al0.3Ga0.7As/In0.25Ga0.75As/GaAs heterostructures for electron transport applications

We have grown high-electron mobility transistor structures in the Al0.3Ga0.7As/In0.25Ga0.75As/GaAs material system with In0.25Ga0.75As channel thicknesses in the range 40-200 Angstrom. We have monitored the onset of channel relaxation using Hall mobility measurements, polychromatic cathodoluminescence mapping, time-resolved photoluminescence, transmission electron microscopy, low-frequency noise,and deep-level transient spectroscopy measurements. It appears that the first relaxation symptom, the Stransky-Krastanow growth mode, is observed only by the last three techniques. This shows that the onset of relaxation is not detected by characterization techniques which measure global properties of the material. On the other hand, it is detected by low-frequency noise, deep-level transient spectroscopy, and transmission electron microscopy measurements, which yield an estimation of the defect density in the material. (C) 1996 American Institute of Physics

Capacitance and drain current deep level transient spectroscopy measurements on molecular beam epitaxy grown GaAs/ln

Modulation doped GaAs/In0·25Ga0·75As/Al0·3Ga0·7As high electron mobility transistor structures were grown using different molecular beam epitaxy growth temperatures and In0·25Ga0·75 As channel thicknesses. Drain current deep level transient spectroscopy (DLTS) and standard capacitance DLTS measurements were carried out on these devices using a Fourier transform technique. The results show that traps in the barrier as well as those in the buffer have an influence on the drain current of such transistors. In addition, a broadening of one of the DLTS peaks was observed for high channel thicknesses and is shown to be related to a high increase in dislocation concentration, as confirmed by cathodoluminescence measurements

Extraction of FET parameters at low drain bias by taking into account the dependence of mobility on 2D electron gas concentration

An original method for the extraction of FET parameters at low drain bias is presented. It is based on a simple linear charge-control model and on a power-law dependence (with an exponent k > 0 for GaAs/AlGaAs MODFET's and k < 0 for Si-MOSFET's) of the low-field mobility-mu on the two-dimensional electron gas (2DEG) concentration n(S), valid in a certain range of gate voltages. Simple analytical expressions for the transfer characteristics I(ds)-V(gs) and g(m)-V(gs) at low drain bias are combined to extract reliable values of the threshold voltage Vt, the power exponent k, the total parasitic series resistance (R(s)+R(d) and an important control parameter-beta'. We verified that the values of beta' and k extracted on a test MODFET at 300 and 77 K agree very well with those deduced directly from Hall measurements on gated Hall-bridge structures. Our analysis is also applied to extract MOSFET parameters at room temperature

Hot carrier effects in AlGaAs/InGaAs high electron mobility transistors: failure mechanisms induced by hot carrier testing

A new failure mechanism of AlGaAs/InGaAs pseudomorphic high electron mobility transistors has been observed after hot carrier de accelerated testing. Hot carrier effects have been characterized by means of gate current measurements and electroluminescence spectroscopy. After accelerated testing, a permanent degradation has been found, consisting of the decrease of drain current I-D, and of the absolute value of the pinch-off voltage V-p, at low drain-source voltage V-DS, resulting in the development of a remarkable ''kink'' in the output characteristics. Direct current, pulsed, and low-frequency ac measurements demonstrate that the failure mechanism consists of the creation of deep levels under the gate which act as electron traps at low gate-to-drain electric fields. Deep level transient spectroscopy and photoinjection measurements reveal the presence of two levels at 0.77 eV and 1.22 eV. The intensity of the 1.22 eV peak is correlated with the degradation observed in stressed devices

Management of Atopic Dermatitis in Adults in Saudi Arabia: Consensus Recommendations from the Dermatological Expert Group

Abdullah Alakeel,1 Afaf Al Sheikh,2,3 Ali A Alraddadi,4– 6 Khalid Mohammed Alattas,7 Maha Aldayel,8 Mohammed Abdulaziz Alajlan,9 Mohammed Al-Haddab,1 Mohammad Almohideb,3,10 Mohamed Fatani,11 Issam R Hamadah,12 Ruaa Alharithy,13,14 Yousef Binamer,15,16 Kim Papp,17 Ahmed Elaraby18 1Department of Dermatology, College of Medicine, King Saud University, Riyadh, Saudi Arabia; 2Division of Dermatology, Department of Medicine, King Abdulaziz Medical City, Riyadh, Saudi Arabia; 3Department of Dermatology, King Saud Bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia; 4Department of Dermatology, Ministry of National Guard-Health Affairs, Jeddah, Saudi Arabia; 5King Abdullah International Research Center, Jeddah, Saudi Arabia; 6King Saud bin Abdulaziz University for Health Sciences, Jeddah, Saudi Arabia; 7King Fahad Central Hospital, Jazan, Saudi Arabia; 8Dammam Medical Complex, Dammam, Saudi Arabia; 9Dermatology Section MSD, King Fahad Medical City, Riyadh, Saudi Arabia; 10King Abdulaziz Medical City, Riyadh, Saudi Arabia; 11Hera General Hospital, Makkah, Saudi Arabia; 12King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia; 13Security Forces Hospital, Riyadh, Saudi Arabia; 14Princess Nourah University, Riyadh, Saudi Arabia; 15Department of Dermatology, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia; 16Department of Dermatology, Alfaisal University, Riyadh, Saudi Arabia; 17Probity Medical Research Inc. and K. Papp Clinical Research Inc., Waterloo, ON, Canada; 18Bachelor of pharmacy, Cairo University, Giza, EgyptCorrespondence: Issam R Hamadah, Email [email protected]; [email protected]: Atopic dermatitis (AD) is a long-term, pruritic, recurrent, systemic, inflammatory skin disorder. In the Middle East region, the burden of AD is understudied, and there is a dearth of AD guideline documents for practitioners.Methods: An expert panel meeting, encompassing 12 dermatologists from the Kingdom of Saudi Arabia (KSA), was congregated to develop evidence- and experience-based consensus recommendations for AD management, especially in adults in KSA. They completed a questionnaire with seven clinical statements, and a consensus was defined when the responses of ≥ 75% of participants coincided.Results: The expert recommendations were as follows: American Association of Dermatology guidelines are to be followed for defining AD; Eczema Area and Severity Index or SCORing atopic dermatitis index may be used to quantify the disease severity; Dermatology Life Quality Index may be used to determine the impact of AD on patients’ quality of life; Atopic Dermatitis Control Tool may be used to assess long-term disease control in AD patients; and the European guidelines are to be followed for the management of AD. In AD patients who are inadequately controlled with topical or systemic therapies, the preferred systemic agent for use either alone or in combination with topical treatments is dupilumab, cyclosporine, methotrexate, phototherapy, or other available systemic treatments that may include mycophenolate mofetil or oral corticosteroids.Conclusion: These expert recommendations assist physicians by providing a reference framework for optimal care of adult AD patients.Keywords: atopic dermatitis, Dermatology Life Quality Index, Eczema Area and Severity Index, SCORing atopic dermatiti