micro cavity photo diode

1. MICROCAVITY PHOTODIODE
SUBMITTED TO-
DR. LINI MATHEW
H.O.D. ELECTRICAL
ENGINEERING DEPARTMENT
NITTTR CHANDIGARH
SUBMITTED BY:
DEEPAK RAVI
ROLL NO:- 162509
ME(I&C) REGULAR

2. CONTENT
• PHOTODIODE
• MICROCAVITY
• MICROCAVITY PHOTODIODE
• SCHEMATIC DIAGRAM
• ADVANTAGES OF MICROCAVITY PHOTODIODE
• DISADVANTAGES OF MICROCAVITY PHOTODIODE
• DESIGN MATERIAL REQUIRED FOR MICROCAVITY
PHOTODIODE
1

3. PHOTODIODE
2

4. PHOTODIODE CONTINUED……..
 A semiconductor p-n junction device whose region of operation is
limited to reverse bias region
 The application of light to the junction results in a transfer of energy
from the incidence travelling light waves to atomic structure, resulting
in an increased level of reverse current
 Produces photocurrent by generating electron-hole pairs, due to the
absorption of light in the intrinsic or depletion region.
 Photocurrent generated is proportional to the absorbed light intensity

6. OPTICAL CAVITY (FABRY-PEROT CAVITY)
5
OPTICAL CAVITY/RESONATING CAVITY/OPTICAL
RESONATOR/MICROCAVITY

7. OPTICAL CAVITY
• OPTICAL CAVITY/RESONATING CAVITY/OPTICAL
RESONATOR
• An arrangement of mirrors that forms a standing wave cavity
resonator for light waves
• Light confined in the cavity reflects multiple times producing standing
waves for certain resonance frequencies
• A beam will reflect a very large number of times with little attenuation.
• Provides positive feedback of photons by reflection at mirrors at either
end of cavity

8. CONTINUED……
• Optical cavities are designed to have a large Q factor
• Most common types of optical cavities consist of two facing plane (flat)
or spherical mirrors.
• Simplest is the plane-parallel or Fabry–Pérot cavity, consisting of two
opposing flat mirrors. While simple, this arrangement is rarely used in
large-scale lasers due the difficulty of alignment
Optical cavities are a major component of lasers, surrounding
the gain medium and providing feedback of the laser light.

9.  Types of two-mirror optical cavities,
with mirrors of various curvatures,
showing the radiation pattern inside
each cavity.

10. Resonance condition
• The standing waves exist only at the frequencies for which the
distance between the mirrors is an Integral number of half of
wavelength .
𝐿 =
λq
2n
Where: L= length between mirror
n refractive index
q=number of modes

11. Values which satisfy the inequality correspond to stable resonators.
0 ≤ 1 −
𝐿
𝑅1
1 −
𝐿
𝑅2
≤ 1
L=LENGTH OF MIRROR
R1&R2 = CARVERTURE OF
MIRRORS
 Only certain ranges of values
for R1, R2, and L produce stable
resonators in which periodic
refocussing of the intracavity
beam is produced.
STABILITY OF OPTICAL CAVITY
 A stable output is obtained when
optical gain is exactly matched by
the losses incurred in the amplifying
medium
 Major losses: absorption and
scattering in the amplifying medium
& at the mirror and Non useful
transmission through the mirror

12. WHY MICROCAVITY IN PHOTODIODE?
Progression towards higher transmission rates in optical
communication requires high speed photo diode AS A DETECTOR
For high quantum efficiency we need thick absorption region
and for larger bandwidth we need thin absorption region
Bandwidth is important phenomenon that can not be compromised
Thin absorption region with optical cavity increases both quantum
efficiency & bandwidth
In this diode a thin absorption region is placed in the middle of
resonant cavity formed by heavily doped wider band gap regions
and reflecting mirrors

13. CONTINUED….
 A resonance is built up in the p-GsAs cavity at those frequency
components of the incoming light
At the resonance frequency the incoming frequency is reflected
at the two mirrors and round trip path is greatly increased
The absorption and the quantum efficiency are therefore
enhanced
This way microcavity photodiode simultaneously achieves both
large bandwidth and high possible quantum efficiency

14. P-GaAs active layer
-
+

15. DESIGN AND MATERIAL
REQUIREMENT
 Mirror and the cavity materials must be non-absorbing at the detection
wavelength
 The mirror should have very high reflectivity so that it gives highest
optical confinement inside the cavity
 The absorption in the cavity can be limited by making the band gap of
the active region smaller than the cavity and the mirror. But a large
difference in the band gap would be a blockage in extraction of photo
generated carriers from a hetero junction
8

16. ADVANTAGES OF MICROCAVITY
PHOTODIODE
Higher quantum efficiency
Higher detection speed
Wavelength selective detection
High bandwidth
Enhanced Absorption and quantum efficiency
7

17. DISADVANTAGES
• Very difficult to manufacture
• High cost

18. APPLICATION OF MICROCAVITY
PHOTODIODE
 As a detector in optical fiber communication
 Used to count items on conveyor belt
 Optical communication devices
 Position sensors
 Bar code scanners
 Automotive devices
 Surveying instruments

19. 978-1-4799-7049-0/14/$31.00 ©2014 IEEE
A Novel MEMS Gas Sensor Based on Ultrasonic
Resonance Cavity
P. J. Koppinen, T. Sillanpa¨a, A. K ¨ arkk ¨ ainen, J.
Saarilahti, and H. Sepp ¨ a¨
Knowledge Intensive Products and Services (KIPS)
VTT Technical Research Centre of Finland
Micronova, Tietotie 3, Espoo, Finland
Email: panu.koppinen@vtt.fi

20. • Abstract—We present a novel low–cost and low–power MEMS
gas sensor concept based on an ultrasonic resonance cavity.
The sensor consists of a capacitive micromachined ultrasonic
transducer (CMUT) embedded to an acoustic resonance cavity.
The sensor operation was demonstrated with carbon dioxide CO2
and methane CH4, the lowest resolvable concentrations are about
10 - 20 ppm – a competitive result with the existing commercially
available CO2 sensors. In addition, the sensor is able to measure
gas concentration and humidity independently, and thus can be
used as a combo sensor for gas concentrations and humidity.

21. REFERENCES
• OPTO-ELECTRONICS DEVICES BY P BHATTACHARYA
• OPTICAL FIBER COMMUNICATION BY G KEISER
• WIKIPEDIA