I am NOT sure that Charles' answer ('incentive pay') is appropriate in the given context. In this connection, please see the following:
1) Incentive pay, also known as "pay for performance" is generally given for specific performance results rather than simply for time worked. While incentives are not the answer to all personnel challenges, they can do much to increase worker performance.
reference:
http://www.cnr.berkeley.edu/ucce50/ag-labor/7labor/08.htm
2) Incentive pay - definition
A wage or salary arrangement in which additional compensation is awarded for performance that exceeds an established benchmark. For example, employees of a company may be rewarded with a proportion of the firm's profits that exceed a specific amount.
see
http://www.yourdictionary.com/business/incentive-pay