<PAGE>   1
                                                                     Exhibit 4.2



                  UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED
REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY TO THE COMPANY OR ITS AGENT FOR
REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS
REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN
AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY (AND ANY PAYMENT
HEREON IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN
AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY), ANY TRANSFER, PLEDGE
OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL SINCE
THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. THIS NOTE IS A
GLOBAL NOTE WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS
REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF. THIS NOTE IS
EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE
DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE
INDENTURE AND, UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR
SECURITIES IN DEFINITIVE FORM, THIS NOTE MAY NOT BE TRANSFERRED EXCEPT AS A
WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE
DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE
DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH
SUCCESSOR DEPOSITARY.

                  THIS NOTE (OR ITS PREDECESSOR) WAS ORIGINALLY ISSUED IN A
TRANSACTION EXEMPT FROM REGISTRATION UNDER THE UNITED STATES SECURITIES ACT OF
1933 (THE "SECURITIES ACT"), AND THIS NOTE AND THE COMMON STOCK ISSUABLE UPON
CONVERSION THEREOF MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED IN THE
ABSENCE OF SUCH REGISTRATION OR AN APPLICABLE EXEMPTION THEREFROM. EACH
PURCHASER OF THIS NOTE IS HEREBY NOTIFIED THAT THE SELLER OF THIS NOTE MAY BE
RELYING ON THE EXEMPTION FROM THE PROVISIONS OF SECTION 5 OF THE SECURITIES ACT
PROVIDED BY RULE 144A THEREUNDER.

                  THE HOLDER OF THIS NOTE AGREES FOR THE BENEFIT OF THE COMPANY
THAT (A) THIS NOTE AND THE NOTE COMMON STOCK ISSUABLE UPON CONVERSION THEREOF
MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE TRANSFERRED, ONLY (I) IN THE UNITED
STATES TO A PERSON WHOM THE SELLER REASONABLY BELIEVES IS A QUALIFIED
INSTITUTIONAL BUYER (AS DEFINED IN RULE 144A UNDER THE SECURITIES ACT) IN A
TRANSACTION MEETING THE REQUIREMENTS OF RULE 144A, (II) OUTSIDE THE UNITED
STATES IN AN OFFSHORE TRANSACTION IN ACCORDANCE WITH RULE 904 UNDER THE
SECURITIES ACT, (III) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE
SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF AVAILABLE) OR (IV) PURSUANT
TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, IN EACH OF
CASES (I) THROUGH (IV) IN ACCORDANCE WITH ANY APPLICABLE SECURITIES LAWS OF ANY
STATE OF THE UNITED STATES, AND (B) THE HOLDER WILL, AND EACH SUBSEQUENT HOLDER
IS REQUIRED TO, NOTIFY ANY PURCHASER OF THIS NOTE FROM IT OF THE RESALE
RESTRICTIONS REFERRED TO IN (A) ABOVE. IN ANY CASE, THE HOLDER HEREOF WILL NOT,
DIRECTLY OR INDIRECTLY, ENGAGE IN ANY HEDGING TRANSACTIONS WITH REGARD TO THE
NOTES EXCEPT AS PERMITTED UNDER THE SECURITIES ACT.





                                       1
<PAGE>   2

                  THE HOLDER OF THIS NOTE IS ENTITLED TO THE BENEFITS OF A
REGISTRATION RIGHTS AGREEMENT (AS SUCH TERM IS DEFINED IN THE INDENTURE REFERRED
TO ON THE REVERSE HEREOF) AND, BY ITS ACCEPTANCE HEREOF, AGREES TO BE BOUND BY
AND TO COMPLY WITH THE PROVISIONS OF SUCH REGISTRATION RIGHTS AGREEMENT.

                  THIS NOTE MAY NOT BE SOLD OR TRANSFERRED TO, AND EACH
PURCHASER BY ITS PURCHASE OF THIS SECURITY SHALL BE DEEMED TO HAVE REPRESENTED
AND COVENANTED THAT IT IS NOT ACQUIRING THIS SECURITY FOR OR ON BEHALF OF, AND
WILL NOT TRANSFER THIS SECURITY TO, ANY PENSION OR WELFARE PLAN AS DEFINED IN
SECTION 3 OF THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974, AS AMENDED
("ERISA") EXCEPT THAT SUCH PURCHASE FOR OR ON BEHALF OF A PENSION OR WELFARE
PLAN SHALL BE PERMITTED:

                  (1) TO THE EXTENT SUCH PURCHASE IS MADE BY OR ON BEHALF OF A
         BANK COLLECTIVE INVESTMENT FUND MAINTAINED BY THE PURCHASER IN WHICH NO
         PLAN (TOGETHER WITH ANY OTHER PLANS MAINTAINED BY THE SAME EMPLOYER OR
         EMPLOYEE ORGANIZATION) HAS AN INTEREST IN EXCESS OF 10% OF THE TOTAL
         ASSETS IN SUCH COLLECTIVE INVESTMENT FUND, AND THE OTHER APPLICABLE
         CONDITIONS OF PROHIBITED TRANSACTION CLASS EXEMPTION 91-38 ISSUED BY
         THE DEPARTMENT OF LABOR ARE SATISFIED;

                  (2) TO THE EXTENT SUCH PURCHASE IS MADE BY OR ON BEHALF OF AN
         INSURANCE COMPANY POOLED SEPARATE ACCOUNT MAINTAINED BY THE PURCHASER
         IN WHICH, AT ANY TIME WHILE THESE SECURITIES ARE OUTSTANDING, NO PLAN
         (TOGETHER WITH ANY OTHER PLANS MAINTAINED BY THE SAME EMPLOYER OR
         EMPLOYEE ORGANIZATION) HAS AN INTEREST IN EXCESS OF 10% OF THE TOTAL OF
         ALL ASSETS IN SUCH POOLED SEPARATE ACCOUNT, AND THE OTHER APPLICABLE
         CONDITIONS OF PROHIBITED TRANSACTION CLASS EXEMPTION 90-1 ISSUED BY THE
         DEPARTMENT OF LABOR ARE SATISFIED;

                  (3) TO THE EXTENT SUCH PURCHASE IS MADE ON BEHALF OF A PLAN BY
         (A) AN INVESTMENT ADVISER REGISTERED UNDER THE INVESTMENT ADVISERS ACT
         OF 1940, AS AMENDED (THE "1940 ACT"), THAT HAD AS OF THE LAST DAY OF
         ITS MOST RECENT FISCAL YEAR TOTAL ASSETS UNDER ITS MANAGEMENT AND
         CONTROL IN EXCESS OF $50.0 MILLION AND HAD STOCKHOLDERS' OR PARTNERS'
         EQUITY IN EXCESS OF $750,000, AS SHOWN IN ITS MOST RECENT BALANCE SHEET
         PREPARED IN ACCORDANCE WITH GENERALLY ACCEPTED ACCOUNTING PRINCIPLES,
         OR (B) A BANK AS DEFINED IN SECTION 202(A)(2) OF THE 1940 ACT WITH
         EQUITY CAPITAL IN EXCESS OF $1.0 MILLION AS OF THE LAST DAY OF ITS MOST
         RECENT FISCAL YEAR, OR (C) AN INSURANCE COMPANY WHICH IS QUALIFIED
         UNDER THE LAWS OF MORE THAN ONE STATE TO MANAGE, ACQUIRE OR DISPOSE OF
         ANY ASSETS OF A PENSION OR WELFARE PLAN, WHICH INSURANCE COMPANY HAS AS
         OF THE LAST DAY OF ITS MOST RECENT FISCAL YEAR, NET WORTH IN EXCESS OF
         $1.0 MILLION AND WHICH IS SUBJECT TO SUPERVISION AND EXAMINATION BY A
         STATE AUTHORITY HAVING SUPERVISION OVER INSURANCE COMPANIES AND, IN ANY
         CASE, SUCH INVESTMENT ADVISER, BANK OR INSURANCE COMPANY IS OTHERWISE A
         QUALIFIED PROFESSIONAL




                                       2
<PAGE>   3

         ASSET MANAGER, AS SUCH TERM IS USED IN PROHIBITED TRANSACTION CLASS
         EXEMPTION 84-14 ISSUED BY THE DEPARTMENT OF LABOR, AND THE ASSETS OF
         SUCH PLAN WHEN COMBINED WITH THE ASSETS OF OTHER PLANS ESTABLISHED OR
         MAINTAINED BY THE SAME EMPLOYER (OR AFFILIATE THEREOF) OR EMPLOYEE
         ORGANIZATION AND MANAGED BY SUCH INVESTMENT ADVISER, BANK OR INSURANCE
         COMPANY, DO NOT REPRESENT MORE THAN 20% OF THE TOTAL CLIENT ASSETS
         MANAGED BY SUCH INVESTMENT ADVISER, BANK OR INSURANCE COMPANY AT THE
         TIME OF THE TRANSACTION, AND THE OTHER APPLICABLE CONDITIONS OF SUCH
         EXEMPTION ARE OTHERWISE SATISFIED;

                  (4) TO THE EXTENT SUCH PLAN IS A GOVERNMENTAL PLAN (AS DEFINED
         AS SECTION 3 OF ERISA) WHICH IS NOT SUBJECT TO THE PROVISIONS OF TITLE
         1 OF ERISA OR SECTION 401 OF THE INTERNAL REVENUE CODE OF 1986, AS
         AMENDED (THE "CODE");

                  (5) TO THE EXTENT SUCH PURCHASE IS MADE BY OR ON BEHALF OF AN
         INSURANCE COMPANY USING THE ASSETS OF ITS GENERAL ACCOUNT, THE RESERVES
         AND LIABILITIES FOR THE GENERAL ACCOUNT CONTRACTS HELD BY OR ON BEHALF
         OF ANY PLAN, TOGETHER WITH ANY OTHER PLANS MAINTAINED BY THE SAME
         EMPLOYER (OR ITS AFFILIATES) OR EMPLOYEE ORGANIZATION, DO NOT EXCEED
         10% OF THE TOTAL RESERVES AND LIABILITIES OF THE INSURANCE COMPANY
         GENERAL ACCOUNT (EXCLUSIVE OF SEPARATE ACCOUNT LIABILITIES), PLUS
         SURPLUS AS SET FORTH IN THE NATIONAL ASSOCIATION OF INSURANCE
         COMMISSIONERS ANNUAL STATEMENT FILED WITH THE STATE OF DOMICILE OF THE
         INSURER, IN ACCORDANCE WITH PROHIBITED TRANSACTION CLASS EXEMPTION
         95-60, AND THE OTHER APPLICABLE CONDITIONS OF SUCH EXEMPTION ARE
         OTHERWISE SATISFIED;

                  (6) TO THE EXTENT PURCHASE IS MADE BY AN IN-HOUSE ASSET
         MANAGER WITHIN THE MEANING OF PART IV(A) OF PROHIBITED TRANSACTION
         CLASS EXEMPTION 96-23, SUCH MANAGER HAS MADE OR PROPERLY AUTHORIZED THE
         DECISION FOR SUCH PLAN TO PURCHASE THIS SECURITY, UNDER CIRCUMSTANCES
         SUCH THAT PROHIBITED TRANSACTION CLASS EXEMPTION 96-23 IS APPLICABLE TO
         THE PURCHASE AND HOLDING OF THIS SECURITY; OR

                  (7) TO THE EXTENT SUCH PURCHASE WILL NOT OTHERWISE GIVE RISE
         TO A TRANSACTION DESCRIBED IN SECTION 406 OR SECTION 4975(C)(1) OF THE
         CODE FOR WHICH A STATUTORY OR ADMINISTRATIVE EXEMPTION IS UNAVAILABLE.





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<PAGE>   4

                               EMCORE CORPORATION

CUSIP: 290846 AA2                                                            R-1

                   5% CONVERTIBLE SUBORDINATED NOTES DUE 2006

                  EMCORE Corporation, a New Jersey corporation (the "Company",
which term shall include any successor corporation under the Indenture referred
to on the reverse hereof), promises to pay to Cede & Co., or registered assigns,
the principal sum of One Hundred Seventy-Five Million Dollars ($175,000,000) on
May 15, 2006 or such greater or lesser amount as is indicated on the Schedule of
Exchanges of Notes on the other side of this Note.

                  Interest Payment Dates:  May 15 and November 15

                  Record Dates:  May 1 and November 1

                  This Note is convertible as specified on the other side of
this Note. Additional provisions of this Note are set forth on the other side of
this Note.

                  IN WITNESS WHEREOF, the Company has caused this instrument to
be duly executed.

                                             EMCORE Corporation

                                             By: /s/ Howard Brodie
                                                --------------------------------
                                             Name: Howard Brodie
                                             Title: Vice President

Attest:


By: /s/ Michael O'Sullivan
   ------------------------------------
Name: Michael O'Sullivan
Title: Assistant General Counsel

Dated:  May 7, 2001
      ---------------------------------

Trustee's Certificate of Authentication: This is one of the Notes referred to in
the within-mentioned Indenture.

WILMINGTON TRUST COMPANY,
as Trustee


By: /s/ James D. Nesci
   -----------------------------------
Name: James D. Nesci
Title: Authorized Signer





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<PAGE>   5
                           [REVERSE SIDE OF SECURITY]

                               EMCORE CORPORATION
                   5% CONVERTIBLE SUBORDINATED NOTES DUE 2006

1. INTEREST

                  EMCORE Corporation, a New Jersey corporation (the "Company",
which term shall include any successor corporation under the Indenture
hereinafter referred to), promises to pay interest on the principal amount of
this Note at the rate of 5% per annum. The Company shall pay interest
semiannually on May 15 and November 15 of each year, commencing November 15,
2001, unless such date is not a business day, in which case, we shall pay
interest on the next succeeding business day and such payment shall be deemed to
have been paid on such interest payment date and no interest shall accrue during
the additional period of time. Interest on the Notes shall accrue from the most
recent date to which interest has been paid or, if no interest has been paid,
from May 7, 2001; provided, however, that if there is not an existing default in
the payment of interest and if this Note is authenticated between a record date
referred to on the face hereof and the next succeeding interest payment date,
interest shall accrue from such interest payment date. Interest will be computed
on the basis of a 360-day year of twelve 30-day months. Any reference herein to
interest accrued or payable as of any date shall include any Additional Interest
accrued or payable on such date as provided in the Registration Rights
Agreement.

2. METHOD OF PAYMENT

                  The Company shall pay interest on this Note (except defaulted
interest) to the person who is the Holder of this Note at the close of business
on May 1 or November 1, as the case may be, next preceding the related interest
payment date. The Holder must surrender this Note to a Paying Agent to collect
payment of principal. The Company will pay principal and interest in money of
the United States that at the time of payment is legal tender for payment of
public and private debts. The Company may, however, pay principal and interest
in respect of any Definitive Note by check or wire payable in such money;
provided, however, that a Holder with an aggregate principal amount in excess of
$2,000,000 will be paid by wire transfer in immediately available funds at the
election of such Holder. The Company may mail an interest check to the Holder's
registered address. Notwithstanding the foregoing, so long as this Note is
registered in the name of a Depositary or its nominee, all payments hereon shall
be made by wire transfer of immediately available funds to the account of the
Depositary or its nominee.

3. PAYING AGENT, REGISTRAR AND CONVERSION AGENT

                  Initially, Wilmington Trust Company, (the "Trustee," which
term shall include any successor trustee under the Indenture hereinafter
referred to) will act as Paying Agent, Registrar and Conversion Agent. The
Company may change any Paying Agent, Registrar or Conversion Agent without
notice to the Holder. The Company or any of its Subsidiaries may, subject to
certain limitations set forth in the Indenture, act as Paying Agent or
Registrar.

4. INDENTURE, LIMITATIONS

                  This Note is one of a duly authorized issue of Notes of the
Company designated as its 5% Convertible Subordinated Notes due 2006 (the
"Notes"), issued under an Indenture dated as of May 7, 2001 (together with any
supplemental indentures thereto, the "Indenture"), between the Company and



                                       5
<PAGE>   6

the Trustee. The terms of this Note include those stated in the Indenture and
those required by or made part of the Indenture by reference to the Trust
Indenture Act of 1939, as amended, as in effect on the date of the Indenture.
This Note is subject to all such terms, and the Holder of this Note is referred
to the Indenture and said Act for a statement of them. All capitalized terms
used but not defined herein shall have the meaning ascribed to such term in the
Indenture.

                  The Notes are subordinated unsecured obligations of the
Company limited to $175,000,000 aggregate principal amount, subject to Section
2.2 of the Indenture. The Indenture does not limit other debt of the Company,
secured or unsecured, including Senior Indebtedness.

5. PROVISIONAL AND OPTIONAL REDEMPTION

                  The Notes may be redeemed at the election of the Company, as a
whole or in part from time to time, at any time prior to May 20, 2004 (a
"PROVISIONAL REDEMPTION"), upon at least 20 and not more than 60 days' notice by
mail to the Holders of the Notes at a redemption price equal to $1,000 per
$1,000 principal amount of the Notes redeemed plus accrued and unpaid interest,
if any (such amount, together with the Make-Whole Payment described below, the
"PROVISIONAL REDEMPTION PRICE"), to but excluding the date of redemption (the
"PROVISIONAL REDEMPTION DATE") if (1) the Closing Sale Price of the Common Stock
has exceeded 150% of the Conversion Price for at least 20 Trading Days within a
period of any 30 consecutive Trading Days ending on the Trading Day prior to the
date of mailing of the notice of Provisional Redemption (the "NOTICE DATE"), and
(2) a shelf registration statement covering resales of the Notes and the Common
Stock issuable upon conversion thereof is effective and available for use and is
expected to remain effective and available for use for the 30 days following the
Provisional Redemption Date unless registration is no longer required.

                  Upon any such Provisional Redemption, the Company, shall make
an additional payment, at its option, in cash or Common Stock or a combination
of cash and Common Stock (the "MAKE-WHOLE PAYMENT") with respect to the Notes
called for redemption to holders on the Notice Date in an amount equal to
$150.00 per $1,000 principal amount of the Notes, less the amount of any
interest actually paid (including, if the Provisional Redemption Date occurs
after a record date but before an interest payment date, any interest paid or
payable in connection with such interest payment date) on such Notes prior to
the Provisional Redemption Date. Payments made in Common Stock will be valued at
97% of the average closing sales prices of Common Stock for the five Trading
Days ending on the day prior to the Redemption Date. The Company shall make the
Make-Whole Payment on all Notes called for Provisional Redemption, including
those Notes converted into Common Stock between the Notice Date and the
Provisional Redemption Date.

                  Except as set forth above, the Notes are subject to
redemption, at any time on or after May 20, 2004, on at least 20 days and no
more than 60 days notice, in whole or in part, at the election of the Company.
The Redemption Prices (expressed as percentages of the principal amount) are as
follows for Notes redeemed during the periods set forth below:

             Period                                      Redemption Price
             ------                                      ----------------

May 20, 2004 through May 14, 2005........................     101.25%
May 15, 2005 and thereafter..............................     100.00%





                                       6
<PAGE>   7

in each case together with accrued interest up to but not including the
Redemption Date; provided that if the redemption date is an interest payment
date, interest will be payable to the Holders in whose names the Notes are
registered at the close of business on the relevant record dates.

6. NOTICE OF REDEMPTION

                  Notice of redemption will be mailed by first-class mail at
least 20 days but not more than 60 days before the Redemption Date to each
Holder of Notes to be redeemed at its registered address. Notes in denominations
larger than $1,000 may be redeemed in part, but only in whole multiples of
$1,000. On and after the Redemption Date, subject to the deposit with the Paying
Agent of funds sufficient to pay the Redemption Price plus accrued interest, if
any, accrued to, but not including, the Redemption Date, interest shall cease to
accrue on Notes or portions of them called for redemption.

7. PURCHASE OF NOTES AT OPTION OF HOLDER UPON A CHANGE IN CONTROL

                  At the option of the Holder and subject to the terms and
conditions of the Indenture, the Company shall become obligated to purchase all
or any part specified by the Holder (so long as the principal amount of such
part is $1,000 or an integral multiple of $1,000 in excess thereof) of the Notes
held by such Holder on the date that is 30 Business Days after the occurrence of
a Change in Control, at a purchase price equal to 100% of the principal amount
thereof together with accrued interest up to, but excluding, the Change in
Control Purchase Date. The Holder shall have the right to withdraw any Change in
Control Purchase Notice (in whole or in a portion thereof that is $1,000 or an
integral multiple of $1,000 in excess thereof) at any time prior to the close of
business on the Business Day next preceding the Change in Control Purchase Date
by delivering a written notice of withdrawal to the Paying Agent in accordance
with the terms of the Indenture.

8. CONVERSION

                  A Holder of a Note may convert the principal amount of such
Note (or any portion thereof equal to $1,000 or any integral multiple of $1,000
in excess thereof) into shares of Common Stock at any time prior to the close of
business on May 15, 2006; provided, however, that if the Note is called for
redemption or subject to purchase upon a Change in Control, the conversion right
will terminate at the close of business on the Business Day immediately
preceding the redemption date or the Change in Control Purchase Date, as the
case may be, for such Note or such earlier date as the Holder presents such Note
for redemption or purchase (unless the Company shall default in making the
redemption payment or Change in Control Purchase Price, as the case may be, when
due, in which case the conversion right shall terminate at the close of business
on the date such default is cured and such Note is redeemed or purchased).

                  The initial Conversion Price is $48.7629 per share, subject to
adjustment under certain circumstances. The number of shares of Common Stock
issuable upon conversion of a Note is determined by dividing the principal
amount of the Note or portion thereof converted by the Conversion Price in
effect on the Conversion Date. No fractional shares will be issued upon
conversion; in lieu thereof, an amount will be paid in cash based upon the
closing price (as defined in the Indenture) of the Common Stock on the Trading
Day immediately prior to the Conversion Date.

                  To convert a Note, a Holder must (a) complete and manually
sign the conversion notice set forth below and deliver such notice to a
Conversion Agent, (b) surrender the Note to a Conversion Agent, (c) furnish
appropriate endorsements and transfer documents if required by a Registrar or a




                                       7
<PAGE>   8

Conversion Agent, and (d) pay any transfer or similar tax, if required. Notes so
surrendered for conversion (in whole or in part) during the period from the
close of business on any regular record date to the opening of business on the
next succeeding interest payment date (excluding Notes or portions thereof
called for redemption or subject to purchase upon a Change in Control on a
Redemption Date or Change in Control Purchase Date, as the case may be, during
the period beginning at the close of business on a regular record date and
ending at the opening of business on the first Business Day after the next
succeeding interest payment date, or if such interest payment date is not a
Business Day, the second such Business Day) shall also be accompanied by payment
in funds acceptable to the Company of an amount equal to the interest payable on
such interest payment date on the principal amount of such Note then being
converted, and such interest shall be payable to such registered Holder
notwithstanding the conversion of such Note, subject to the provisions of this
Indenture relating to the payment of defaulted interest by the Company. If the
Company defaults in the payment of interest payable on such interest payment
date, the Company shall promptly repay such funds to such Holder. A Holder may
convert a portion of a Note equal to $1,000 or any integral multiple thereof.

                  A Note in respect of which a Holder had delivered a Change in
Control Purchase Notice exercising the option of such Holder to require the
Company to purchase such Note may be converted only if the Change in Control
Purchase Notice is withdrawn in accordance with the terms of the Indenture.

9. SUBORDINATION

                  The indebtedness evidenced by the Notes is, to the extent and
in the manner provided in the Indenture, subordinate and junior in right of
payment to the prior payment in full in cash of all Senior Indebtedness. Any
Holder by accepting this Note agrees to and shall be bound by such subordination
provisions and authorizes the Trustee to give them effect. In addition to all
other rights of Senior Indebtedness described in the Indenture, the Senior
Indebtedness shall continue to be Senior Indebtedness and entitled to the
benefits of the subordination provisions irrespective of any amendment,
modification or waiver of any terms of any instrument relating to the Senior
Indebtedness or any extension or renewal of the Senior Indebtedness.

10. DENOMINATIONS, TRANSFER, EXCHANGE

                  The Notes are in registered form without coupons in
denominations of $1,000 and integral multiples of $1,000. A Holder may register
the transfer of or exchange Notes in accordance with the Indenture. The
Registrar may require a Holder, among other things, to furnish appropriate
endorsements and transfer documents and to pay any taxes or other governmental
charges that may be imposed in relation thereto by law or permitted by the
Indenture.

11. PERSONS DEEMED OWNERS

                  The Holder of a Note may be treated as the owner of it for all
purposes.

12. UNCLAIMED MONEY

                  If money for the payment of principal or interest remains
unclaimed for two years, the Trustee or Paying Agent will pay the money back to
the Company at its written request. After that, Holders entitled to money must
look to the Company for payment.




                                       8
<PAGE>   9

13. AMENDMENT, SUPPLEMENT AND WAIVER

                  Subject to certain exceptions, the Indenture or the Notes may
be amended or supplemented with the consent of the Holders of at least a
majority in principal amount of the Notes then outstanding, and an existing
default or Event of Default and its consequence or compliance with any provision
of the Indenture or the Notes may be waived in a particular instance with the
consent of the Holders of a majority in principal amount of the Notes then
outstanding. Without the consent of or notice to any Holder, the Company and the
Trustee may amend or supplement the Indenture or the Notes to, among other
things, cure any ambiguity, defect or inconsistency or make any other change
that does not adversely affect the rights of any Holder.

14. SUCCESSOR CORPORATION

                  When a successor corporation assumes all the obligations of
its predecessor under the Notes and the Indenture in accordance with the terms
and conditions of the Indenture, the predecessor corporation will (except in
certain circumstances specified in the Indenture) be released from those
obligations.

15. DEFAULTS AND REMEDIES

                  Under the Indenture, an Event of Default includes: (i) default
for 30 days in payment of any interest on any Notes; (ii) default in payment of
any principal (including, without limitation, any premium, if any) on the Notes
when due; (iii) failure by the Company for 60 days after notice to it to comply
with any of its other agreements contained in the Indenture or the Notes; (iv)
we fail to comply with any of the provisions of Section 6.09 of the Indenture;
(v) we fail to provide timely notice of a change in control; and (vi) certain
events of bankruptcy, insolvency or reorganization of the Company. If an Event
of Default (other than as a result of certain events of bankruptcy, insolvency
or reorganization of the Company) occurs and is continuing, the Trustee or the
Holders of at least 25% in principal amount of the Notes then outstanding may
declare all unpaid principal to the date of acceleration on the Notes then
outstanding to be due and payable immediately, all as and to the extent provided
in the Indenture. If an Event of Default occurs as a result of certain events of
bankruptcy, insolvency or reorganization of the Company, unpaid principal of the
Notes then outstanding shall become due and payable immediately without any
declaration or other act on the part of the Trustee or any Holder, all as and to
the extent provided in the Indenture. Holders may not enforce the Indenture or
the Notes except as provided in the Indenture. The Trustee may require indemnity
satisfactory to it before it enforces the Indenture or the Notes. Subject to
certain limitations, Holders of a majority in principal amount of the Notes then
outstanding may direct the Trustee in its exercise of any trust or power. The
Trustee may withhold from Holders notice of any continuing default (except a
default in payment of principal or interest) if it determines that withholding
notice is in their interests. The Company is required to file periodic reports
with the Trustee as to the absence of default.

16. TRUSTEE DEALINGS WITH THE COMPANY

                  Wilmington Trust Company, the Trustee under the Indenture, in
its individual or any other capacity, may make loans to, accept deposits from
and perform services for the Company or an Affiliate of the Company, and may
otherwise deal with the Company or an Affiliate of the Company, as if it were
not the Trustee.



                                       9
<PAGE>   10

17. NO RECOURSE AGAINST OTHERS

                  A director, officer, employee or shareholder, as such, of the
Company shall not have any liability for any obligations of the Company under
the Notes or the Indenture nor for any claim based on, in respect of or by
reason of such obligations or their creation. The Holder of this Note by
accepting this Note waives and releases all such liability. The waiver and
release are part of the consideration for the issuance of this Note.

18. AUTHENTICATION

                  This Note shall not be valid until the Trustee or an
authenticating agent manually signs the certificate of authentication on the
other side of this Note.

19. ABBREVIATIONS AND DEFINITIONS

                  Customary abbreviations may be used in the name of the Holder
or an assignee, such as: TEN COM (= tenants in common), TEN ENT (= tenants by
the entireties), JT TEN (= joint tenants with right of survivorship and not as
tenants in common), CUST (= Custodian) and UGMA (= Uniform Gifts to Minors Act).

                  All terms defined in the Indenture and used in this Note but
not specifically defined herein are defined in the Indenture and are used herein
as so defined.

20. INDENTURE TO CONTROL; GOVERNING LAW

                  In the case of any conflict between the provisions of this
Note and the Indenture, the provisions of the Indenture shall control. This Note
shall be governed by, and construed in accordance with, the laws of the State of
New York, without regard to principles of conflicts of law.

                  The Company will furnish to any Holder, upon written request
and without charge, a copy of the Indenture. Requests may be made to: EMCORE
Corporation, 145 Belmont Drive, Somerset, New Jersey 08873, Attention: Chief
Financial Officer.




                                       10
<PAGE>   11
                                 ASSIGNMENT FORM

To assign this Note, fill in the form below:

I or we assign and transfer this Note to


--------------------------------------------------------------------------------
                  (Insert assignee's soc. sec. or tax I.D. no.)


--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
              (Print or type assignee's name, address and zip code)


and irrevocably appoint


--------------------------------------------------------------------------------

agent to transfer this Note on the books of the Company. The agent may
substitute another to act for him or her.



                                           Your Signature:


Date:
     -------------------------------       -------------------------------------
                                           (Sign exactly as your name appears
                                           on the other side of this Note)


*Signature guaranteed by:


By:
   -------------------------------------


*        The signature must be guaranteed by an institution which is a member of
         one of the following recognized signature guaranty programs: (i) the
         Securities Transfer Agent Medallion Program (STAMP); (ii) the New York
         Stock Exchange Medallion Program (MSP); (iii) the Stock Exchange
         Medallion Program (SEMP); or (iv) such other guaranty program
         acceptable to the Trustee.




                                       11
<PAGE>   12
                                CONVERSION NOTICE

To convert this Note into Common Stock of the Company, check the box: [ ]



To convert only part of this Note, state the principal amount to be converted
(must be $1,000 or a multiple of $1,000):
$____________ .


If you want the stock certificate made out in another person's name, fill in the
form below:


--------------------------------------------------------------------------------
                  (Insert assignee's soc. sec. or tax I.D. no.)



--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
              (Print or type assignee's name, address and zip code)




                                           Your Signature:


Date:
     -------------------------------       -------------------------------------
                                           (Sign exactly as your name appears
                                           on the other side of this Note)


*Signature guaranteed by:


By:
   -------------------------------------

*        The signature must be guaranteed by an institution which is a member of
         one of the following recognized signature guaranty programs: (i) the
         Securities Transfer Agent Medallion Program (STAMP); (ii) the New York
         Stock Exchange Medallion Program (MSP); (iii) the Stock Exchange
         Medallion Program (SEMP); or (iv) such other guaranty program
         acceptable to the Trustee.



                                       12
<PAGE>   13
               OPTION TO ELECT REPURCHASE UPON A CHANGE OF CONTROL


To: EMCORE Corporation

         The undersigned registered owner of this Note hereby irrevocably
acknowledges receipt of a notice from EMCORE Corporation (the "Company") as to
the occurrence of a Change in Control with respect to the Company and requests
and instructs the Company to redeem the entire principal amount of this Note, or
the portion thereof (which is $1,000 or an integral multiple thereof) below
designated, in accordance with the terms of the Indenture referred to in this
Note at the Change in Control Purchase Price, together with accrued interest to,
but excluding, such date.

Dated:
      ----------------------------             ---------------------------------

                                               ---------------------------------
                                               Signature(s)


                                               Signature(s) must be guaranteed
                                               by a qualified guarantor
                                               institution with membership in an
                                               approved signature guarantee
                                               program pursuant to Rule 17Ad-15
                                               under the Securities Exchange Act
                                               of 1934.


                                               ---------------------------------
                                               Signature Guaranty

Principal amount to be redeemed
(in an integral multiple of $1,000, if less than all):


------------------------------
NOTICE: The signature to the foregoing Election must correspond to the Name as
written upon the face of this Note in every particular, without alteration or
any change whatsoever.



                                       13
<PAGE>   14

                         SCHEDULE OF EXCHANGES OF NOTES

         The following exchanges, redemptions, repurchases or conversions of a
part of this global Note have been made:



<TABLE>
<CAPTION>
 Principal Amount of
  this Global Note
    Following Such
  Decrease Date of                                    Amount of Decrease in         Amount of Increase in
    Exchange (or            Authorized Signatory       Principal Amount of           Principal Amount of
     Increase)                 of Custodian              this Global Note              this Global Note
 -------------------        --------------------      ---------------------         ---------------------
<S>                         <C>                       <C>                           <C>




</TABLE>





                                       14
<PAGE>   15


            CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION
                  OF TRANSFER OF TRANSFER RESTRICTED SECURITIES

Re:      5% Convertible Subordinated Notes due 2006 (the "Notes") of
         EMCORE Corporation.

         This certificate relates to $_______ principal amount of Notes owned
         in (check applicable box)

         [ ] book-entry or  [ ] definitive form by _________________________
         (the "Transferor").

         The Transferor has requested a Registrar or the Trustee to exchange or
register the transfer of such Notes.

         In connection with such request and in respect of each such Note, the
Transferor does hereby certify that the Transferor is familiar with transfer
restrictions relating to the Notes as provided in Section 2.12 of the Indenture
dated as of May 7, 2001 between EMCORE Corporation and Wilmington Trust Company,
(the "Indenture"), and the transfer of such Note is being made pursuant to an
effective registration statement under the Securities Act of 1933, as amended
(the "Securities Act") (check applicable box) or the transfer or exchange, as
the case may be, of such Note does not require registration under the Securities
Act because (check applicable box):

[ ]      Such Note is being transferred pursuant to an effective registration
         statement under the Securities Act.

[ ]      Such Note is being acquired for the Transferor's own account, without
         transfer.

[ ]      Such Note is being transferred to the Company or a Subsidiary (as
         defined in the Indenture) of the Company.

[ ]      Such Note is being transferred to a person the Transferor reasonably
         believes is a "qualified institutional buyer" (as defined in Rule 144A
         or any successor provision thereto ("Rule 144A") under the Securities
         Act) that is purchasing for its own account or for the account of a
         "qualified institutional buyer", in each case to whom notice has been
         given that the transfer is being made in reliance on such Rule 144A,
         and in each case in reliance on Rule 144A.

[ ]      Such Note is being transferred pursuant to and in accordance with Rule
         903 or Rule 904 under the Securities Act and, accordingly, the
         Transferor hereby further certifies that (i) the transfer is not being
         made to a person in the United States and (x) at the time the buy order
         was originated, the transferee was outside the United States or such
         Transferor and any Person acting on its behalf reasonably believed and
         believes that the transferee was outside the United States or (y) the
         transaction was executed in, on or through the facilities of a
         designated offshore securities market and neither such Transferor nor
         any Person acting on its behalf knows that the transaction was
         prearranged with a buyer in the United States, (ii) no directed selling
         efforts have been made in contravention of the requirements of Rule
         903(b) or Rule 904(b) of Regulation S under the Securities Act and
         (iii) the transaction is not part of a plan or scheme to evade the
         registration requirements of the Securities Act and (iv) if the
         proposed transfer is being made prior to the expiration of the
         Restricted Period, the transfer is not being made to a U.S. Person or
         for the account or benefit of a U.S. Person (other than an Initial
         Purchaser).

[ ]      Such Note is being transferred pursuant to and in compliance with an
         exemption from the registration requirements under the Securities Act
         in accordance with Rule 144 (or any successor thereto) ("Rule 144")
         under the Securities Act.

[ ]      Such Note is being transferred pursuant to and in compliance with an
         exemption from the registration requirements of the Securities Act
         (other than an exemption referred to above) and as a result of which





                                       15
<PAGE>   16

         such Note will, upon such transfer, cease to be a "restricted security"
         within the meaning of Rule 144 under the Securities Act.

         The Transferor acknowledges and agrees that, if the transferee will
hold any such Notes in the form of beneficial interests in a global Note which
is a "restricted security" within the meaning of Rule 144 under the Securities
Act, then such transfer can only be made pursuant to Rule 144A under the
Securities Act and such transferee must be a "qualified institutional buyer" (as
defined in Rule 144A).



Date:
     -------------------------------           ---------------------------------
                                                   (Insert Name of Transferor)





                                       16