Laser Cooling in Semiconductors

Chengao Wang

Optical Science and Engineering,

Department of Physics & Astronomy, University of New Mexico

Historical Review

1929: The concept of laser cooling was established.

1960: Laser was invented. 1995: Laser cooling was first observed in

ytterbium-doped glass. ????: Laser cooling in semiconductors is

achieved.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Significance

Heating is a major problem in semiconductor devices.

Optical refrigerator using laser cooling will be free of vibration, mechanically robust and compact.

It has far reaching implications in the area of optical detection systems and optoelectronic devices.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Purpose

invent a practical all-solid-state optical refrigerator to cool semiconductors using laser cooling.

We hypothesize that laser cooling in semiconductors can achieve temperatures ~10K and below

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Overview of Methodology

1. Develop a comprehensive theoretical model of laser cooling in semiconductors.

2. Grow new semiconductor materials optimized for laser cooling using MOCVD

3. Demonstrate experimentally the theory of laser cooling in semiconductor devices.

4. Build prototype optical refrigerator in semiconductors.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

The concept of laser cooling

Cooling Cycle

phonons

phonons

1

2

4

excited state

ground state

3

Laser fhh

OPTICAL SCIENCE & ENGINEERING University of New Mexico

The concept of laser cooling in semiconductors

Pump

Semiconductorheterostructure

h hf

Valence band

Conduction band

Eg

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Step 1: Develop a comprehensive theoretical model of laser cooling in

semiconductors. Two key issues, luminescence trapping and

red-shifting, have not been addressed in the current theory and these issues will frustrate our attempts to achieve semiconductor net cooling

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Luminescence Trapping

Total internal reflection

Pump

semiconductor

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Luminescence red-shift

( )f f f f

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Step1: Deliverable

understanding of which materials are optimum for laser cooling in semiconductors.

predict the possible designs of the future optical refrigerators.

Step 2: Use MOCVD to grow new semiconductor materials

InGaP/GaAs Heterostructures have been predicted to be good candidates for laser cooling in semiconductors.

perform microscopic analysis of each material in order to optimize the materials for laser cooling.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Step2: Deliverable

optimal materials that have a good chance of achieving net cooling.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Step 3: Demonstrate experimentally the theory of laser cooling in semico

nductor devices

Do experiment to prove laser cooling in semiconductors

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Step3: Deliverable

proof of net cooling in semiconductors reevaluating our theory about laser cooling i

n semiconductors and further optimizing the materials.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Step 4: Build prototype optical refrigerator in semiconductors.

In order to build a practical devise, we should first solve some engineering issues.

After making the preliminary optical refrigerator, we may try to make it more compact and efficient.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Step4: Deliverable

an infant machine for practical applications.

OPTICAL SCIENCE & ENGINEERING University of New Mexico

The Goal: An All-Solid-State Cryocooler

The research involve all fundamental physics and engineering issues of laser cooling in solids that will pave the way for the development of a practical all-sold-state optical cryocooler.

Refrigerant solid

fluorescencefluorescence

heat sinkheat sink

laserlaser

cold fingerelement

•All-solid-state (rugged, compact)

•No vibrations (no moving parts or fluids)

•Efficient

•For space-based sensors

OPTICAL SCIENCE & ENGINEERING University of New Mexico

Thank you