Deserts or semi-deserts are usually felt as not very interesting ecosystem by many people. Nevertheless, there are many animals and plant species living there. These species show often very interesting adaptations to extreme environment conditions.
Deserts and xeric shrublands is an ecosystem characterized by, relating to, or requiring only a small 
amount of moisture. Deserts and xeric shrublands receive an annual average rainfall of ten inches or less, and have an arid or hyperarid climate, characterized by a strong moisture deficit, where annual potential loss of moisture from evapotranspiration well exceeds the moisture received as rainfall. Deserts and xeric shrublands occur in tropical, subtropical, and temperate climate regions. Desert soils tend to be sandy or rocky, and low in organic materials. Saline or alkaline soils are common. Plants and animals in deserts and xeric shrublands are adapted to low moisture conditions. Hyperarid regions are mostly devoid of vegetation and animal life, and include rocky deserts and sand dunes . Vegetation in arid climate regions can include sparse grasslands, shrublands, and woodlands. Plants adapted to arid climates are called xerophytes, and include succulent plants, geophytes, sclerophyll, and annual plants. Animals, including insects, reptiles, arachnids, birds and mammals, are frequently nocturnal to avoid moisture loss.
Deserts take up about one fifth of the Earth's land surface. Hot deserts usually have a large diurnal and seasonal temperature range, with high daytime temperatures, and low nighttime temperatures (due to extremely low humidity). In hot deserts the temperature in the daytime can reach 45 °C/113 °F or higher in the summer, and dip to 0 °C/32°F or lower in the winter. Water acts to trap infrared radiation from both the sun and the ground, and dry desert air is incapable of blocking sunlight during the day or trapping heat during the night. Thus, during daylight most of the sun's heat reaches the ground, and as soon as the sun sets the desert cools quickly by radiating its heat into space. Urban areas in deserts lack large (more than 14 °C/25 °F) daily temperature variations, partially due to the urban heat island effect.
Many deserts are formed by rain shadows; mountains blocking the path of precipitation to the desert. Deserts are often composed of sand and rocky surfaces. Sand dunes called ergs and stony surfaces called hamada surfaces compose a minority of desert surfaces. Exposures of rocky terrain are typical, and reflect minimal soil development and sparseness of vegetation.
Bottomlands may be salt-covered flats. Eolian processes are major factors in shaping desert landscapes. Cold deserts (also known as polar deserts) have similar features, except the main form of precipitation is snow rather than rain. Antarctica is the world's largest cold desert (composed of about 98 percent thick continental ice sheet and 2 percent barren rock). Some of the barren rock is to be found in the so-called Dry Valleys of Antarctica that almost never get snow, which can have ice-encrusted saline lakes that suggest evaporation far greater than the rare snowfall due to the strong katabatic winds that evaporate even ice.
The largest hot desert is the Sahara.
Deserts sometimes contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Due to extreme and consistent dryness, some deserts are ideal places for natural preservation of artifacts and fossils.
Ecosystem of semi-desert is not strictly defined. Usually it is considered as a transitional zone between real deserts and grasslands. Vegetation does not cover the surface fully like in grasslands but it is much more lusher comparing with a desert.
Albatros Travel and Expeditions can provide you many trips directed into desert and semi-desert areas worldwide. These trips are usually easy. Even not trained people can take part in such journeys. There is a list of countries where deserts and semi-deserts can be visited:
Chile - almost exclusively parks in the northern part of the country
Ecuador - rarely in Central Andes and in Galapagos