9. STOCK- BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Stock-based compensation expense by line item
Stock-based compensation expense	$ 2,070,000	$ 1,877,000	$ 1,850,000
Other information
Income tax benefit recognized from allocation of share-based compensation expense	0	0
Windfall tax benefits realized	0	0
Unrecognized compensation costs	$ 4,000,000
Weighted average period of recognition of unrecognized compensation costs	2 years 7 days
Cost of revenues
Stock-based compensation expense by line item
Stock-based compensation expense	$ 259,000	282,000	320,000
Research and development
Stock-based compensation expense by line item
Stock-based compensation expense	1,141,000	980,000	858,000
Selling, general and administrative
Stock-based compensation expense by line item
Stock-based compensation expense	670,000	615,000	672,000
2007 Employee Stock Purchase Plan
Stock-based compensation expense by line item
Stock-based compensation expense	$ 207,000	$ 150,000	$ 136,000