An array of highly efficient micro-LEDs (100) and a manufacturing process are described. Each micro-LED (100) is an integrated diode structure in a mesa (105), in which the mesa shape and the light-emitting region (104) are chosen for optimum efficiency. A single one of the micro-LEDs (100) comprises, on a substrate (101) and a semiconductor layer (102), a mesa (103), a light emitting layer (104), and an electrical contact (106). The micro-LEDs in this device have a very high EE because of their shape. Light is generated within the mesa, which is shaped to enhance the escape probability of the light. Very high EEs are achieved, particularly with a nearparabolic mesa that has a high aspect ratio. The top of the mesa is truncated above the light-emitting layer (LEL), providing a flat surface for the electrical contact (106) on the top of the semiconductor mesa. It has been found that the efficiency is high provided the top contact has a good reflectivity value. Also, it has been found that efficiency is particularly high if the contact (106) occupies an area of less than 16% of the truncated top mesa surface area. This feature also helps to achieve a more directional beam in the case of the device being an LED.