11. STOCK-BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($)	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Stock-based compensation expense by line item
Stock-based compensation expense	$ 2,262,000	$ 2,838,000	$ 2,469,000
Cost of revenues
Stock-based compensation expense by line item
Stock-based compensation expense	199,000	228,000	202,000
Research and development
Stock-based compensation expense by line item
Stock-based compensation expense	1,010,000	1,411,000	1,316,000
Selling, general and administrative
Stock-based compensation expense by line item
Stock-based compensation expense	1,053,000	1,199,000	951,000
Employee Stock Purchase Plan Year 2007
Stock-based compensation expense by line item
Stock-based compensation expense	$ 176,000	$ 230,000	$ 211,000