They weren't created out of jealousy, but out of impatience. In chapter 2 of the Quenta Silmarillion, it says:
It is told that in their beginning the Dwarves were made by Aulë in the darkness of Middle-earth; for so greatly did Aulë desire the coming of the Children, to have learners to whom he could teach his lore and his crafts, that he was unwilling to await the fulfillment of the designs of Iluvatar.
And later, when Ilúvatar found out about his creation and asked him why he acted beyond his authority:
Then Aulë answered: 'I did not desire such lordship. I desired things other than I am, to love and to teach them, so that they too might perceive the beauty of Eä, which thou hast caused to be.1 For it seemed to me that there is great room in Arda for many things that might rejoice in it, yet it is for the most part empty still, and dumb.
It's important to note that Aulë was well-intentioned and meant no harm: he even offers to destroy his works:
[']I offer to thee these things, the work of the hands which thou hast made. Do with them what thou wilt. But should I not rather destroy the work of my presumption?'
Then Aulë took up a great hammer to smite the Dwarves; and he wept. But Ilúvatar had compassion upon Aulë and his desire, because of his humility; [...] And the voice of Ilúvatar said to Aulë: 'Thy offer I accepted even as it was made. Dost thou not see that these things have now a life on their own, and speak with their own voices?[' ...] Then Aulë cast down his hammer and was glad, and he gave thanks to Ilúvatar, saying: 'May Eru bless my work and amend it!'
Note 1This echoes a passage out of Friedrich Nietzsche's Thus Spoke Zarathustra:
Companions the creator seeks, not corpses, not herds and believers. Fellow creators the creator seeks—those who write new values on new tablets. Companions the creator seeks, and fellow harvesters; for everything about him is ripe for the harvest.