The upper bands (or buckets) in good lasing materials such as gallium arsenide are narrow and have steep sides, so they tend to hold relatively few electrons.

• 在砷化镓等发光效率较高的雷射材料中，上层能带（或桶子）相当窄，两侧曲线很陡，因此可容纳的电子数目比较少；