<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0304</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2012-02-24</periodOfReport>

    <dateOfOriginalSubmission>2012-02-28</dateOfOriginalSubmission>

    <issuer>
        <issuerCik>0000808326</issuerCik>
        <issuerName>EMCORE CORP</issuerName>
        <issuerTradingSymbol>EMKR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001265677</rptOwnerCik>
            <rptOwnerName>WEINSWIG MARK</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EMCORE CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>10420 RESEARCH ROAD, SE</rptOwnerStreet2>
            <rptOwnerCity>ALBUQUERQUE</rptOwnerCity>
            <rptOwnerState>NM</rptOwnerState>
            <rptOwnerZipCode>87123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Emcore Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2012-02-24</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2448</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.41</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8474</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired through the EMCORE Corporation 2000 Employee Stock Purchase Plan in a transaction exempt from Section 16(b) pursuant to Rule 16b-3(d).</footnote>
        <footnote id="F2">On February 28, 2012, the reporting person filed a Form 4 that erroneously coded this acquisition as transaction code P instead of transaction code A.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Alfredo Gomez, attorney-in-fact</signatureName>
        <signatureDate>2012-03-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
