问题 问答题 简答题

两种高速的光电二极管的结构特点和原理?(PIN、APD)

答案

参考答案:

PIN光电二极管结构特点:P层和N层之间增加了一层很厚的高电阻率的本征半导I

增加I区优点:(1)因为I区相对的P区和N区是高阻,在反偏的工作情况下,它承受极大部分电压降,使耗尽区增大,这样展宽了光电转换有效工作区,使灵敏度增大(2)又因为PIN结光电二极管的工作电压是很高的反偏电压,使PIN结的耗尽层加宽,电场强光生电流加速因而大幅度减少了载流子在结构内漂移时间元件的响应速度加快。

电路特点:反偏电压高。

APD光电二极管结构特点:在光照时P+层受光子能量激发的电子从所带电跃迁到导带,在高电场作用下,电子从高速通过P层产生碰撞电离,形成大量新生电子空穴对,并且它们也从电场中获得高能量与从P+层来的电子一起再次碰撞P区的其他原子,又产生大批新生电子。

单项选择题
阅读理解

Federal Child Labor Standards for Teenagers

Teenage labor in the United States

Federal Law sets child labor standards affecting teenage workers in the private companies and in federal, state, and local governments.

How can injuries be prevented?

Demand Training

Insist on adequate supervision(监督)and easy access to a supervisor at all times.

Demand sufficient training on equipment and chemicals you are required to use.Refuse to use unknown materials or machinery that is broken or improperly set up.

Wear protective equipment

Always use whatever protective equipment is supplied.Protective clothing includes non-slip shoes, gloves and other specific job-related protective gear.

Request reasonable protective equipment if it is not provided automatically.

Know your environment

Ask about workplace hazards and precautions(预防措施)that can help prevent injuries.

Workplace hazards are objects and situations present at your job that could potentially hurt you.Recognize safety hazards such as slippery floors, unsafe ladders, sharp knives, and heavy lifting.

Know the law

Learn about federal and state laws governing employment for teenagers and make you’re your supervisor enforces them.

How many working hours are allowed?

Teenagers (ages 14-15) may total no more than

■3 hours on a school day.

■18 hours in a school week.(A school week is any week in which school attendance is required for any part of four or more days.)

■8 hours on a non-school day.

■40 hours m a non-school week.

What are the responsibilities?

Employers and employees share the responsibility for keeping the workplace safe and healthy.As a teenage worker, you can do your part by taking these steps:

■Follow rules.

■Use safety equipment.

■Keep your work area clean.

■Report all injuries.

■Inform a supervisor if you feel sick.

■Report safety problems.

小题1:If a teenager is asked to work with equipment out of order, he or she should       _.

A.demand enough training

B.refuse to work with the equipment

C.ignore the instructions on the machine

D.ask for necessary protective tools小题2:All of these are examples of workplace hazards EXCEPT        .

A.sharp knives

B.heavy lifting

C.slippery floors

D.steady ladders小题3:According to the passage, which of the following should a teenage worker do in the workplace?

A.Depend on his own in any case.

B.Deal with his injuries himself.

C.Contact a supervisor when feeling uncomfortable.

D.Use any tool in hand.