subclass_of backward diode
A ___MASK88___ ___MASK60___ or Esaki ___MASK60___ is a type of semiconductor that is capable of very fast operation , well into the ___MASK22___ frequency region , made possible by the use of the quantum mechanical effect called tunneling . In semiconductor devices , a backward ___MASK60___ ( also called back ___MASK60___ ) is a variation on a Zener ___MASK60___ or tunnel ___MASK60___ having a better conduction for small reverse biases ( for example -- 0 . 1 to -- 0 . 6 V ) than for forward bias voltages . The reverse current in such a ___MASK60___ is by tunneling , which is also known as the tunnel effect . ___MASK11___ is the number of occurrences of a repeating event per unit ___MASK54___ . It is also referred to as temporal frequency , which emphasizes the contrast to spatial frequency and angular frequency . The period is the duration of ___MASK54___ of one ___MASK39___ in a repeating event , so the period is the reciprocal of the frequency . For example , if a newborn baby ' s heart beats at a frequency of 120 times a minute , its period  the ___MASK54___ interval between beats  is half a ___MASK24___ ( that is , 60 seconds divided by 120 beats ). ___MASK11___ is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena , such as mechanical vibrations , audio ( sound ) signals , radio waves , and light . In ___MASK38___ , a diode is a two - terminal ___MASK70___ that conducts primarily in one direction ( asymmetric conductance ); it has low ( ideally zero ) resistance to the flow of current in one direction , and high ( ideally infinite ) resistance in the other . A ___MASK44___ , the most common type today , is a crystalline piece of semiconductor material with a p  n junction connected to two electrical terminals . A vacuum tube diode has two electrodes , a plate ( anode ) and a heated cathode . Semiconductor diodes were the first semiconductor electronic devices . The discovery of crystals ' rectifying abilities was made by German physicist Ferdinand Braun in 1874 . The first semiconductor diodes , called cat ' s whisker diodes , developed around 1906 , were made of mineral crystals such as galena . Today , most diodes are made of silicon , but other semiconductors such as selenium or germanium are sometimes used . A Zener ___MASK60___ allows current to flow from its anode to its cathode like a normal ___MASK44___ , but it also permits current to flow in the reverse ___MASK53___ when its " Zener ___MASK100___ " is reached . Zener diodes have a highly doped p - n ___MASK55___ . Normal diodes will also break down with a reverse ___MASK100___ but the ___MASK100___ and sharpness of the knee are not as well defined as for a Zener ___MASK60___ . Also normal diodes are not designed to operate in the breakdown region , but Zener diodes can reliably operate in this region . Semiconductors are crystalline or amorphous solids with distinct electrical characteristics . They are of high ___MASK94___  higher than typical resistance materials , but still of much lower resistance than insulators . Their resistance decreases as their temperature increases , which is behavior opposite to that of a metal . Finally , their conducting properties may be altered in useful ways by the deliberate , controlled introduction of impurities (" doping ") into the crystal structure , which lowers its resistance but also permits the creation of semiconductor junctions between differently - doped regions of the extrinsic semiconductor crystal . The behavior of charge carriers which include electrons , ions and electron holes at these junctions is the basis of diodes , transistors and all modern electronics . Microwaves are a form of ___MASK62___ with wavelengths ranging from one meter to one millimeter ; with frequencies between and . This broad definition includes both UHF and EHF ( millimeter wave ) bands , and various sources use different boundaries . In all cases , microwaves include the entire SHF band ( 3 to 30 GHz , or 10 to 1 cm ) at minimum , with RF ___MASK64___ often restricting the ___MASK52___ between 1 and 100 GHz ( 300 and 3 mm ). Frequencies in the microwave ___MASK52___ are often referred to by their IEEE radar band designations : S , ___MASK61___ , X , K , K , or K band , or by similar NATO or EU designations .