This electrical detection technique is simple, fast, and convenient. The deâ tecting signal ...... www.the-infoshop.com/report/fd139268-us-chemical-sensor.html.
1 [email protected] http://nina.ecse.rpi.edu/shur/. GaN Microwave Transistors. Michael S. Shur. Rensselaer Polytechnic Institute. Presented at NJIT on 11/09/05 ...
AbstractâWe report a successful application of atomic layer deposition (ALD) aluminum oxide as a passivation layer to gallium nitride high electron-mobility ...
May 17, 2007 - heating and improved reliability and operating stability. AlGaN/GaN HEMTs grown on SiC substrates are very promising for high power, high ...
AlGaN/GaN HEMTs are well-suited to high-frequency and high-power applications [1, 2]. SiC is presently the substrate of choice for high-performance GaN ...
Self-aligned T-gate AlGaN/GaN high electron mobility transistors. (HEMTs) were fabricated on a sapphire substrate using a thin. Ti/Al/Ti/Au ohmic layer.
Keywords: - AlGaN/GaN HEMT; Nonalloyed Ohmic contacts; Selective area growth ... GaN-based high electron mobility transistors (HEMTs) have attracted much ...
Nov 6, 2013 - transistors on low dislocation density bulk GaN substrate: Implications of surface step edges. N. Killat. H. H. Wills Physics Laboratory, Nicole.
The eGaNÂ® FET. Journey Continues .... MOSFET. Module. 40 V/ 30 V. EPC Gen 4. V. IN. =12 V V. OUT. =1.2 V 1 MHz. DC-DC .... SiC n-MOSFET. CPM2-1200- ...
helped me a lot getting familiar with equipment as well as being always patient in answering my questions ...... project is to develop a stress methodology which can reveal the activation energy of device degradation ... geometry of the gate is a sta
Nov 21, 2017 - strate is conductive, the electric field around the drain is formed along the vertical ... the drain current by conductivity modulation. The injection.
gem on drain voltage in the linear regime shows linear increase in acoustic transconductance, while floor remains mainly unchanged. (c) Dependence of gem ...
semi-insulating GaN templates for nitride high electron mobility transistors by using the large ... an AlN/GaN HEMT structure was first grown by molecular.
Introduction: GaN-based transistors attract significant attention from .... not only by the gate breakdown but also by the avalanche breakdown under the drain.
Jun 1, 2000 - given by. Dn,m n* m x dr, and G (Em. En) is the Lorentzian function given by. G Em. En. Em .... and F000629 from the US Office of Naval Research. The ... 7 Y. F. Wu, S. Keller, P. Kozodoy, B. P. Keller, P. Parikh, D. Kapolnek, S.
Dec 6, 2016 - GaN thin films are grown by hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) at 200 C. TFTs exhibit 103 on-to-off current ...
Jan 1, 2015 - 2.1 Field plates structure for HEMT device. ..... At the AlGaN/GaN interface, the conduction band is lower than the Fermi level with zero bias.
May 16, 2007 - random alloy scattering from the AlGaN barrier, an N-face GaN-spacer HEMT was designed with an epi- structure consisting of an AlGaN ...
Gallium nitride. Nakamura and blue light. Higher current, higher goal. Thank you, Yoder, thank you all. (A poem dedicated to the MRS Panel in the fall of 1998, ...
Physical models for GaN optoelectronic applications. â¢ Optical application examples. â¢ Random compositional variation effects. â¢ Blue LED. â¢ Triple quantum well ...
TiO2(001) grown on wurtzite GaN(0001) by radio-frequency O2-plasma molecular beam epitaxy. Two studies are ... titanium dioxide system, which can have applications as a high-k dielectric gate insulator for Si- based devices1. .... The interface betwe
measurement), and Lpads is the transfer length from source and drain contact pads (2 Î¼m in the calculation). The calculated. Ron,spâVbk curve is plotted and ...
blue InGaN / GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with and without an additional n-doped In0.18Ga0.82N electron reservoir layer ...
GaN based transistors
FP FP dielectric G D SiO2
AlxGa1-xN barrier i-GaN
Transistors "The Transistor was probably the most important invention of the 20th Century…” The American Institute of Physics Nobel Prizes: 1956 The prize was awarded jointly, one third each, to: WILLIAM SHOCKLEY, JOHN BARDEEN and WALTER HOUSER BRATTAIN for their researches on semiconductors and their discovery of the transistor effect. 2000 The prize is being awarded with one half jointly to: ZHORES I. ALFEROV, and HERBERT KROEMER for developing semiconductor heterostructures used in high-speed- and opto-electronics and one half to: JACK ST. CLAIR KILBY for his part in the invention of the integrated circuit
First Transistor, 1947
First Integrated Circuit, 1958
Intel’s 1.7 Billion Transistor Chip 2004
Field-Effect Transistor (FET) principles Metal
Lots of electrons
Lots of electrons – high S-D current
No electrons – no S-D current
FET principles Any FET device is very similar to a plain capacitor
Let the area of the capacitor plates be A. The induced charge Q can be expressed as Q = q × A × ∆nS, where q = 1.6 ×10-19 C is the electron charge, ∆nS is the SURFACE CONCENTRATION of induced electrons, ∆nS = Q / (q × A); What is the surface concentration? The bulk charge density, n the layer thickness, a; then the surface concentration, nS = n × a
1x1 cm2 a
Estimation of induced charge Metal V
For the PLAIN CAPACITOR, C = ε ε0 ×A/d Q = C × V = ε ε0 ×A×V/d, The charge per unit area, Q1 = ε ε0 ×V/d The induced concentration of electrons in the top (metal) plate: ∆nSM = - ε ε0 ×V/(q×d) <0 (depletion) in the bottom (semiconductor) plate: ∆nS = ε ε0 ×V/(q×d) >0 (accumulation)
Estimation of the induced charge ε = εr×ε0; For the gap filled with dielectric, εr = 10; ε0 = 8.85×10-12 F/m; Let d = 0.1 µm; V = 10 V; ∆nS = εr ε0 ×V/(q×d) |∆ns| ≈ 5.53×1014 m-2 = 5.53 × 1012 cm-2; In semiconductor films, the nS ≈ 1011 - 1013 cm-2; In 1 µm thick metal film, nSM ≈ 1019 cm-2 >>|∆nS|; • No conductivity modulation in the metal plate • Significant conductivity modulation in the semiconductor film • In this example, the semiconductor film with the equilibrium surface electron concentration of 5× 1012 cm-2 would be completely depleted by applying 10 V at the gate
The threshold voltage of FETs Suppose the semiconductor plate is doped with donor concentration ND; The equilibrium electron concentration in the semiconductor, n0 = ND; For the layer thickness, a, the surface concentration nS0 = ND ×a; The voltage needed to deplete the entire active layer ( the semiconductor plate) is referred to as the THRESHOLD VOLTAGE of the FET For the n-doped layer the threshold voltage is negative in order to repulse the electrons. The induced concentration at the threshold has to compensate the equilibrium one: ∆nST = ε ε0 ×VT/(q×d) = - nS0 Therefore, VT = - q×d ×nS0/ (ε ε0)
The charge control model of FETs
At the threshold the net concentration in the channel is zero: ∆nST – nS0 = 0, where ∆nST = ε ε0 ×VT/(q×d) When the applied gate voltage is above the threshold, VG > VT, ∆nS = ε ε0 ×VG/(q×d) nS = ∆nS – ∆nST = ε ε0 /(q×d) × (VG – VT) Note, ε ε0 /d = C1 the gap capacitance per unit area Therefore,
nS = (C1/q) × (VG – VT) The above model is referred to as “charge control model” of FETs
FET channel current The current through the channel is
VD I= R
The gate length LG
+ where VD is the voltage applied between the DRAIN and the SOURCE
We are assuming that VD << VT The channel resistance, R (Z is the device width, a is the channel thickness):
LG LG = R= q n µ a Z q ns µ Z The channel current :
q ns (VG ) ⋅ µ ⋅ Z VD I= LG
FET transconductance In the amplifier circuit, the input signal is applied at the gate, the drain current modulates the output voltage. The transconductance, gm = dI/dVG measures the amplifier gain.
q ns (VG ) µ Z I= VD LG
q ns 0 µ Z gm = VD | VT | ⋅LG
The main factors affecting FET performance (for any FET type):
ns, µ LG
I and gm I and gm
Highest carrier concentration and mobility in the channel and shortest gate length are key performance parameters of any FET
FET speed of response The gate length LG
The time it takes the electrons to drift under the gate:
LG tdr = vS vS is the electron saturation velocity (limited by scattering) The corresponding FET cutoff frequency,
1 vS fT = = 2π tdr 2π LG High speed operation requires short gate length and high electron velocity.
Effects of high drain bias on FET characteristics MOSFET
The gate- to drain voltage difference depends on the position along the gate So does the induced charge
Effects of high drain bias on FET characteristics
The particular range of the gate voltage depends on the device type
The channel narrowing at the drain edge of the gate causes current saturation in the FETs
Effects of high drain bias on FET characteristics Electron velocity saturation due to high electric field in the channel
Velocity saturation due to high electric field in the channel also results in the I-V saturation
The average electric field in the channel, Eav ~ VD /L Can be extremely high for small L I = V0 µ Z C1 × (VG – VT) /L
I = vS Z C1 × (VG – VT)
v = µ × E ~ µ × VD /L
Different types of FETs Metal - Oxide - Semiconductor FET (MOSFET) d
The gate-channel insulator is made out of dielectric (SiO2), ε = 3.9
Different types of FETs Junction FET (JFET)
The gate-channel insulator consists of the DEPLETION REGION, i.e. the same material as the channel. For GaAs, ε ~ 12; for GaN ε ~ 9.
Different types of FETs
Metal-Semiconductor FET (MESFET)
The gate is formed by Schottky barrier to the semiconductor layer. The gate-channel insulator consists of the DEPLETION REGION, i.e. the same material as the channel. Very similar to the JFET
Performance limitations in FETs Doping dependence of carrier mobility (Si)
Mobility/velocity degradation at high nS results in poor gm and fT
q ns 0 µ Z VD | VT | LG
1 v = S 2π tdr 2π LG
The mechanism of mobility degradation in highly doped layers 1) Mobility depends on the interactions between electrons and phonons and impurities. For the phonon scattering, the dependence of mobility on temperature:
For the impurity scattering, the dependence of mobility on impurity concentration, N:
When the dependence on both temperature and impurities is taken into account,
The mechanism of mobility degradation in highly doped layers Concentration dependence of electron mobility
T = 300 K
The mechanism of velocity degradation in highly doped layers Electron Drift velocity The electron accelerates in the electric field until it gains enough energy to excite lattice vibrations:
m n v n2 max = E n − E o ≈ hω l 2 where vnmax is the maximum electron drift velocity. Then the scattering process occurs, and the electron loses all the excess energy and all the drift velocity. Hence, the electron drift velocity varies between zero and vnmax, and average electron drift velocity (vn = vnmax/2) becomes nearly independent of the electric field:
hω l = v sn 2m n
Typically, vsn ≈ 105 m/s. Indeed, the measured drift velocity becomes nearly constant in high electric fields
The mechanism of mobility degradation in highly doped layers Electron Drift velocity 3 InGaAs
electron velocity (100,000 m/s)
Heavily doped Si
T = 300 K 0 0
electric field (kV/cm)
In the heavily doped materials the peak electron velocity is lower
Performance limitations in FETs Any type of FET using channel doping to provide high channel currents suffers from transconductance/speed of response degradation Channel
Doping increases nS and channel current increase Electron mobility and velocity decrease
gm and fT increase slowly or decrease JFET, MOSFET, MESFET