Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

EFFICIENCY ENHANCEMENT OF INDIRECT GAP LIGHT-EMITTING DEVICES

IP.com Disclosure Number: IPCOM000023710D
Original Publication Date: 1978-Dec-31
Included in the Prior Art Database: 2004-Mar-31
Document File: 2 page(s) / 535K

Publishing Venue

Xerox Disclosure Journal

Abstract

Light-emitting devices are commonly fabricated using semicon-ductor materials having both direct and indirect forbidden energy gaps- In the latter, the lowest empty conduction states do not have the same crystal momentum as the highest filled valence states, For such indirect band gap semicon-ductors, the emission wavelength is determined by the amount of defects (normally chemical impurities) in the host semicon-ductor, There is continuing effort to increase the efficiency of these devices, A scheme is proposed here whereby the efficiency for any light-emitting device fabricated from an indirect gap semiconductor host can have its efficiency enhanced, The enhancement is obtained by applying an external electromagnetic field in the region (normally field-free) where electron-hole recombination occurs, The efficiency increase depends on the field strength along a critical crystallographic direction characterized by the host material and dopant.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 51% of the total text.

Page 1 of 2

XEROX DISCLOSURE JOURNAL

EFFICIENCY ENHANCEMENT OF Proposed Classification
INDIRECT GAP LIGHT-EMITTING tLS~ Cl, 357/17
DEVICES mt. Cl. ROll 33/00
Robert S, Bauer

Light-emitting devices are commonly fabricated using semicon-
ductor materials having both direct and indirect forbidden
energy gaps~ In the latter, the lowest empty conduction
states do not have the same crystal momentum as the highest
filled valence states, For such indirect band gap semicon-
ductors, the emission wavelength is determined by the amount
of defects (normally chemical impurities) in the host semicon-
ductor, There is continuing effort to increase the efficiency
of these devices, A scheme is proposed here whereby the
efficiency for any light-emitting device fabricated from an
indirect gap semiconductor host can have its efficiency
enhanced, The enhancement is obtained by applying an external
electromagnetic field in the region (normally field-free)
where electron-hole recombination occurs, The efficiency
increase depends on the field strength along a critical
crystallographic direction characterized by the host material
and dopant.

The key for producing light emitters from indirect gap solids
has been to choose the proper type and amount of dopant to
fabricate a lower energy direct-gap across which electrons and
holes can radiatively recombine. If a field is applied in the
correct crystallographic direction, the effective density of
direct-gap extrinsic states can be significantly increased,
As a result, the luminescent output will increase, The
physical principle involved is that the electric field gives
an electron extra momentum rendering recombination effective
with the highest energy hole, thereby emitting a photon,

The device structure must be such as to have the rad~ative
recombination occur in a high field region (around 10 V/cm
for an electric field) . In homostructure diodes only some 10%
of the emission occurs in the depletion region where the field
already is high, There are then at least two possibilities
for having most of the recombination in the presence of a
field, Following injection across the p-n junction, the
excited electron could drift into a back-biased high field

Volume 3 Number 6 November/December 1978 445

[This page contai...