Internal id of record is showing blank on matrix item creation

Hi,

On Matrix item creation, record id is returning blank using api nlapiGetRecordId() .
I am creating matrix item manually, i am using following code on after submit event on item creation.After creation of item, creating record in custom record but for matrix item creation the record id is getting blank so can not create in custom record .

function InventoryTabAfterSubmit(type)
{
if (nlapiGetRecordId() > 0) // getting value blank for Matrix item but getting record id for other item type.
{
if (type == 'create')
{
var record = nlapiCreateRecord('customrecord_avaitemmapping');
AVA_ItemSet = 'T'

if(AVA_ItemSet == 'T')
{
nlapiLogExecution('DEBUG', 'AVA_InventoryTabAfterSubmit','nlapiGetRecordId() = '+nlapiGetRecordId());