Ion Implanted Ohmic Contacts to AlGaN/GaN … · From the course syllabus Basic literature & figure sources: G. Rizzoni, Fundamentals of Electrical Engineering, McGraw-Hill R.F. Pierret,

Electronics- lectures for Mechanical Engineering

part 2

Dr. Bogusław Boratyński

Faculty of Microsystems Electronics and Photonics,

Wroclaw University of Technology,

2011

From the course syllabus

Basic literature & figure sources:

G. Rizzoni, Fundamentals of Electrical Engineering, McGraw-Hill

R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publ.,

B.G. Streetman, Solid State Electronic Devices, Prentice-Hall,

D. Bell, Fundamentals of Electric Circuits, Oxford Univ. Press,

T. Mouthaan, Semiconductor Devices Explained, John Willey&Sons

Additional literature:

W. Marciniak, Przyrządy półprzewodnikowe i układy scalone, WNT,

A. Świt, J. Pułtorak, Przyrządy półprzewodnikowe, WNT,

B.G. Streetman, Przyrządy półprzewodnikowe, WNT

Semiconductor devices

Chapter 3 Electronic devices.

3.1 The p-n junction. Semiconductor diodes.

The p-n junction operation principle.

The Shockley equation – the I-V characteristic.

Ideal and real diodes. Temperature effects.

Bias - operating point. Small signal models.

Breakdown in the junction – Zener diode.

Photodiodes and photovoltaic cells.

Metal-semiconductor contact - the Schottky diode.

Rectifier and voltage regulator circuits.

The p-n diode fabrication

Source: R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publishing Comp.

Photolithography process

The ideal p-n junction

A real diode and the ideal p-n junction model

- external bias voltage VA


In p-type sc.:

majority carriers

- holes

In n-type sc.:

majority carriers

- electrons

A-anode

p-type

K-cathode

n-type

symbol

The ideal p-n junction electrostatics


W - the depletion region

(junction region) width

Vo < Eg /q

Typical values: Vo (Eg)

Ge: 0.4V (0.7eV)

Si: 0.7V (1.1eV)

Build-in potential,

or diffusion barrier,

or contact potential

in the p-n junction

Electric field

E

majority

holes

majority

electrons

Forward bias:

diffusion of

majority

carriersReverse bias:

drift of

minority

carriers

Vo

actual barrier

Vo - VA < Vo

actual barrier

Vo + |VA| > Vo

VA >0

VA <0

E

E

The ideal p-n junction at equilibrium and under bias

Energy band models under external bias voltage - VA

minority

holes

I-V characteristic

minority

electrons


Energy band models – another view

a p-n junction formation a p-n junction under bias

Source: T. Mouthaan, Semiconductor Devices Explained,

John Willey&Sons

The ideal p-n junction under bias

The Shockley equation - current-voltage dependence in the p-n junction

Io =const. - saturation current ( due to minority carriers flow)


ln(I) - V

characteristic

exponential function dependence in forward direction

kT/q = 26 mV

@ T=300K

Temperature influence on the I-V characteristic

The Shockley equation – temperature dependence

Io =const. If T=const. but, if T then Io

Temperature coefficients (TC):

Forward voltage - Voltage TC

dV/dT = -2 mV/K @ I=const.

Reverse current - Current TC

(dI/dT)(1/I) = +10%/K @ V=const.

every dT=10K the reverse current doubles

Example (Si diode) at forward bias: dT=70K

at 25 C VA = 620mV @ I = const. (1mA)

at 95 C VA =620mV + 70K · (-2 mV/K) = 620mV - 140mV=

=480mV = 0.48V dVA = -140mV

Example at reverse bias:

at 25 C Irev = 10nA @ VA = const. (-20V)

at 95 C Irev = 27 x 10nA = 128 x 10nA= 1.28 A

kT/q = 26 mV

only @ T=300K

Application:

Diode as a temperature sensor.

A real p-n junction under bias

The Shockley equation + breakdown phenomena at reverse bias

Source: R.F. Pierret, Semiconductor Device Fundamentals,

Addison-Wesley Publishing Comp.

Source: B.G.Streetman, Solid State Electronic Devices,

Prentice Hall.

Breakdown – rapid current increase

a typical

Si diode

I-V curve


The Shockley equation gives a good aproximation of the forward I-V curve.


Prentice Hall.

The diffusion barrier

(junction built-in potential):

Vo < Eg /q

Typical values: Vo (Eg)

Ge: 0.4V (0.7eV)

Si: 0.7V (1.1eV)

GaAs: 1.0V (1.4eV) The „knee voltage” value vs. Eg

similar to Vo- Eg dependence

„knee voltages”





Prentice Hall.

The Shockley equation + additional Rec. - Gen. currents

Junction breakdown – rapid

current increase

- generation

current

Additional

junction

currents:

- recombination

current

A real p-n diode

BAV19 diode

I-V measurements

Io = Ig – generation current

at reverse bias

n –ideality factor

n {1,2}

value dependent on

recombination current

at forward bias

Absolute Maximum Rating from the datasheet:

IF=500mA - dc forward current

VR = 100V - dc reverse voltage

Tj=175C - junction temperature

A real p-n diode

Fairchild BAV19, -20, -21 diodes

DC circuit analysis

The load line concept Finding the operating point - Qpoint

Source: G. Rizzoni, Fundamentals of Electrical Engineering,

McGraw-Hill

from KVL:

VT= RT iD + vD

and the load line equation is:

iD = -(1/ RT) vD + VT /RT

Operating point is;

iD = 21mA , vD = 1.0 V

Small signal equvalent model of a diode

From the Shockley equation:




Prentice Hall.

g = dI/dU = IQ/(kT/q) = IQ/26mV

g-1 = rd - dynamic resistance of the diode

Ctotal - capacitances of a diode

Rseries - parasitic series resistances

Valid for

low frequency:

f<100kHz

Valid for

high frequency:

f>100kHz

g-1 = rd

Rseries

Qp1

Qp2

slope=

g2

slope = g1

Values of the model components depend

on the operating point Q (the applied bias),

excluding Rseries

original single electron

original single electron1+3 electrons

+3 holes

P-N junction breakdown phenomena

Zener breakdown (electron tunneling)



avalanche breakdown

(carrier multiplication)

small voltage bias

no breakdown

large voltage bias

E E

A Zener diode – voltage regulator device

The Zener diode operates at the breakdown at a given voltage Vz

The I-V curve - makes the output voltage constant at Vz


Prentice Hall.

Vz = Zener breakdown voltage

Izm - max. current value

large ripples small ripples

Vz = const.

Input voltage Output voltage

Izm ------------

Rs

Voltage regulator circuit

+_

Vz examples

3.3 V

5 V

6.3 V

9.1 V

12 V

15 V

24 V

91 V

BZX85C9V1

BZX85B12tolerance:

C - 5%

B - 2%

Forward

„self biased”

Solar cell

A photodiode structure



Reverse biased

photodiode

photons

G - flux of photons

Optical absorption in a photodiode

I-V characteristic of illuminated diode

Photon absorption mechanism

Source: T. Mouthaan, Semiconductor Devices Explained,

John Willey&Sons.

0

depletion region

with an electric field

el. field

profile

photon

absorption

- optical absorption constant of the material

Photon absorption

Optical spectrum and the absorption edge λG for various semiconductors



GaN

IRUV

AlGaAs InGaAs

λG [ m]=1.24/Eg [eV]

A photodiode structure

Optical absorption in a photodiode



Reverse biased photodiode

photons

Solar cells



Solar cell becomes forward biased due to illumination – no external bias applied

- power source or power converter

- photocurrent

Forward bias: V>0, but I<0

P= I U < 0 - source of power

Forward

„self biased”

Solar cell

G - flux of photons

I-V characteristics of an illuminated diode

Reverse biased

photodiode

P>0 P<0

Solar cells



Solar cell operationSolar spectum: AM1 - outside atm.

AM 1.5 - av. terrestrial P=100mW/cm sq.

Efficiency:

FF - fill factorPin = Psun

= 5…..15…..30……40 [%}

= 5% amorphous sc.

= 10% polycrystalline sc.

= 20% single crystal sc.

= 35% multi-junction cells

= 40% concentrated sunlight

Max. power point

- operating point

slope

1/R load

R load

Vm

Im

A metal - semiconductor junction

Source: Source: B.G.Streetman, Solid State Electronic Devices, Prentice Hall. Source: J. Singh, Semiconductor Devices , John Willey&Sons

ohmic contact

- small resistance

a Schottky junction

rectifying contact – a diode

- saturation current

thermionic current

Metal Semiconductor

Metal Semiconductor

p-n

diode

General rectifier circuits

Full-wave rectifier circuitHalf-wave rectifier circuit source voltage (f=60Hz, T=1/f=16.7ms)

Source: G.Rizzoni, Fundamentals of Electrical Eng., McGraw-Hill

Rectifier circuits + filtering

Bridge rectifier circuit


1k

RL

1k

RL

Rectifier circuits - constant voltage power supply

DC power supply circuit


Bridge rectifier circuit

large ripples small ripples

Vz = const.

Input voltage Output voltage

Izm ------------

Rs

voltage regulator (Zener diode)

Diodes and their applications

Different types of diodes - summary

Zener diode - voltage regulators

General purpose diode (rectifying, switching)

Electroluminescent diode, LED – display, indicator, lamps

Varactor diode - tuned circuits

Schottky diode (metal-semiconductor diode) – rectifying,

switching also in microwave circuits

Photodiode – photodetector, photovoltaic cell, solar cell

Documents

Ion Implanted Ohmic Contacts to AlGaN/GaN … · From the course syllabus Basic literature & figure sources: G. Rizzoni, Fundamentals of Electrical Engineering, McGraw-Hill R.F. Pierret,